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Prunus and Oemleria (Rosaceae) Flowers from the Late Early Eocene Republic Flora of Northeastern Washington State, U.S.A.

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Two genera of Rosaceae are described from the latest early Eocene Republic flora of northeastern Washington State, United States. Prunus cathybrownae sp. nov. (Rosaceae: subfamily Spiraeoideae, tribe Amygdaleae sensu Potter et al.) is based on eight flowers, including one containing in situ pollen and two immature fruits. Flowers are actinomorphic, perigynous, and pentamerous, with a campanulate hypanthium bearing five sepals. The gynoecium is unicarpellate and consists of a distally flared, bilobed stigma; an elongate style; and an ellipsoid, bilaterally asymmetric ovary. Two whorls of stamens—an inner one in which stamens are reflexed and an outer whorl of extended stamens—are both inserted into the hypanthium. Pollen from the outer whorl is 20 μm in diameter and tricolporate with a striately ornamented exine; clusters of smaller, presumably immature grains 7 μm long and 4 μm wide lacking distinctive ornamentation were recovered from the inner whorl. Immature fruits differ from the flowers in either having a senescent style or lacking one entirely and having fewer remnants of perianth parts and a larger and more symmetrical ovary. A second flower, Oemleria janhartfordae sp. nov. (Rosaceae: subfamily Spiraeoideae, tribe Osmaronieae sensu Potter et al.) is actinomorphic and perigynous and has five free pistils that each resemble the solitary pistil of Prunus. These include a flattened, bilobed stigma and an ellipsoid, bilaterally asymmetric ovary. The fossil has the laterally fixed, elongate style characteristic of the genus. These fossils are the oldest known floral examples of these two genera and demonstrate that both Prunus and Oemleria were present in the latest early Eocene in western North America. The Okanogan Highlands floristic province provides the earliest fossil evidence to date for the first major radiation of the Rosaceae, an important mostly temperate, mostly Northern Hemisphere family.
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Prunus and Oemleria (Rosaceae) Flowers from the Late Early Eocene Republic Flora of
Northeastern Washington State, U.S.A.
Author(s): John C. Benedict, Melanie L. DeVore, and Kathleen B. Pigg
Reviewed work(s):
Source:
International Journal of Plant Sciences,
Vol. 172, No. 7 (September 2011), pp. 948-958
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/10.1086/660880 .
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PRUNUS AND OEMLERIA (ROSACEAE) FLOWERS FROM THE LATE EARLY EOCENE
REPUBLIC FLORA OF NORTHEASTERN WASHINGTON STATE, U.S.A.
John C. Benedict,
1
,
* Melanie L. DeVore,
y
and Kathleen B. Pigg*
*School of Life Sciences, Arizona State University, P.O. Box 874501, Tempe, Arizona 85287, U.S.A.; and
y
Department of Biological and
Environmental Sciences, Georgia College and State University, Campus Box 081, Milledgeville, Georgia 31062, U.S.A.
Two genera of Rosaceae are described from the latest early Eocene Republic flora of northeastern
Washington State, United States. Prunus cathybrownae sp. nov. (Rosaceae: subfamily Spiraeoideae, tribe
Amygdaleae sensu Potter et al.) is based on eight flowers, including one containing in situ pollen and two
immature fruits. Flowers are actinomorphic, perigynous, and pentamerous, with a campanulate hypanthium
bearing five sepals. The gynoecium is unicarpellate and consists of a distally flared, bilobed stigma; an elongate
style; and an ellipsoid, bilaterally asymmetric ovary. Two whorls of stamens—an inner one in which stamens
are reflexed and an outer whorl of extended stamens—are both inserted into the hypanthium. Pollen from the
outer whorl is 20 mm in diameter and tricolporate with a striately ornamented exine; clusters of smaller,
presumably immature grains 7 mm long and 4 mm wide lacking distinctive ornamentation were recovered from
the inner whorl. Immature fruits differ from the flowers in either having a senescent style or lacking one entirely
and having fewer remnants of perianth parts and a larger and more symmetrical ovary. A second flower,
Oemleria janhartfordae sp. nov. (Rosaceae: subfamily Spiraeoideae, tribe Osmaronieae sensu Potter et al.) is
actinomorphic and perigynous and has five free pistils that each resemble the solitary pistil of Prunus. These
include a flattened, bilobed stigma and an ellipsoid, bilaterally asymmetric ovary. The fossil has the laterally fixed,
elongate style characteristic of the genus. These fossils are the oldest known floral examples of these two genera
and demonstrate that both Prunus and Oemleria were present in the latest early Eocene in western North
America. The Okanogan Highlands floristic province provides the earliest fossil evidence to date for the first
major radiation of the Rosaceae, an important mostly temperate, mostly Northern Hemisphere family.
Keywords: Amygdaloideae, fossil flower, hypanthium, Okanogan Highlands, Osmaronieae, Amygdaleae.
Introduction
The family Rosaceae has a good fossil record that extends
from the early Eocene on in Europe and North America
(Kirchheimer 1973; Mai 1984, 1995; DeVore and Pigg 2007).
Although the record is predominantly of compressed leaves,
fossil fruits, wood, and pollen attributed to the family are
also known. The family is particularly well represented in the
early Eocene Republic flora of northeastern Washington State
and other Okanogan Highlands floras of cent ral British
Columbia (Wehr and Hopkins 1994; Greenwood et al. 2005).
More than a dozen rosaceous genera are represented in these
mostly temperate ‘upland’ floras, including extant genera,
forms similar but not identical to extant genera, and others
that are completely extinct (Wehr and Hopkins 1994; De-
Vore and Pigg 2007).
Perhaps the most frequently encountered leaf type in the
flora belongs to the genus Prunus L. These leaves show
a range of variability that has yet to be described in detail;
however, four to five different types were informally recog-
nized by J. Wolfe (W. Wehr, Burke Museum of Natural His-
tory and Culture, personal communication, 2000). Some bear
nectar glands that resemble those characteristic of many ex-
tant Prunus leaves (DeVore and Pigg 2007).
Prunus first appears in the fossil record in the early Eocene
in western North America and Europe and also has a distinct
presence in the Holocene, where endocarps and pollen are of-
ten found within archeological settings (Anderson and Muller
1975; Pollmann et al. 2005). However, to date no fossil
flowers of this genus have been described. Until recently, the
oldest presumed record of Prunus reproductive structures
was a report of endocarp casts from the Paleocene of western
North America assigned to Prunus corrigus Brown (Brown
1962). Recently, these fossil fruits have been reinterpreted as
members of the Icacinaceae (Pigg et al. 2008). A single endo-
carp from the lower Eocene of the Wilcox group of the south-
eastern United States was described as Prunus nabortensis
Berry, and an associated flower type, Antholithes pruniformis
Berry, was interpreted as being related to this fruit (Berry
1916, 1930). Both of these specimens are in need of restudy.
The Eocene of northwestern North America currently pro-
vides our oldest reliable record of Prunus fruits. Permineral-
ized endocarps are known from the latest early to earliest
middle Eocene Princeton chert of central British Columbia,
Canada (Cevallos-Ferriz and Stockey 1991) and the slightly
younger Clarno Nut Beds of Oregon (Manchester 1994). En-
docarps preserved mostly as casts have been reported from
numerous Tertiary sites in Europe from the Eocene on (Kirch-
1
Author for correspondence; e-mail: john.benedict@asu.edu.
Manuscript received December 2010; revised manuscript received May 2011.
948
Int. J. Plant Sci. 172(7):948–958. 2011.
Ó 2011 by The University of Chicago. All rights reserved.
1058-5893/2011/17207-0010$15.00 DOI: 10.1086/660880
heimer 1973; Mai 1984, 1995; Collinson et al. 1993). Rosa-
ceous wood with the characteristic features of Prunus,in-
cluding traumatic resin ducts, is known from Clarno, the
Princeton chert, and the Eocene of Yellowstone National Park
in Wyoming (Wheeler et al. 1978; Cevallos-Ferriz and Stockey
1990; Wheeler and Manchester 2002). Stratigraphically youn-
ger occurrences of fossil rosaceous wood have been reviewed
(Wheeler and Manchester 2002; Wheeler and Dillhoff 2009).
Rosaceous fossil pollen accepted by Muller (1981) has
been described from the Oligocene and lower Miocene of
Cameroon (Salard-Cheboldaeff 1978), the upper Miocene of
northwest Borneo (Anderson and Muller 1975), the Pliocene
of Germany (Menke 1976), and the Pliocene of the Nether-
lands (Zagwijn 1960). Earlier occurrences are less substan-
tiated, although Taylor (1990) notes an occurrence in the
Eocene of California (Frederiksen 1983), and Zetter et al.
(1999) tentatively assign grains from the Eocene of Argentina
to the family. In the Okanogan Highlands, Rosaceae has been
identified in a preliminary same-grain study of the Princeton
chert (Zetter 2004) as well as in pollen profiles based on light
microscopy (LM) alone (Dillhoff et al. 2005; Greenwood
et al. 2005; Moss et al. 2005).
To date, the only floral remains of Rosaceae known from
the Okanogan Highlands are the permineralized flowers of
Paleorosa similkameenensis Basinger that occur in the Prince-
ton chert (Basinger 1976; Cevallos-Ferriz et al. 1993). Paleo-
rosa is an extinct genus that combines traditional characters
delimiting the two traditional subfamilies Spiraeoideae and
Maloideae. The genus was assigned to Spiraeoideae on the
basis of having a follicle as its fruit type; however, similarities
to Maloideae were noted in floral morphology, seed vascula-
ture, and pollen morphology (Cevallos-Ferriz et al. 1993). Its
strongest similarities to an extant genus were noted to be
with Pyracantha Roemer.
In this report, we describe Prunus cathybrownae Benedict,
DeVore, & Pigg, sp. nov. (Rosaceae: subfamily Spiraeoideae,
tribe Amygdaleae sensu Potter et al. 2007), the first reliable
Prunus flowers and young fruits to be recognized in the Ter-
tiary record. The species is based on eight specimens of later-
ally compressed flowers, one of which contains in situ pollen,
and two young fruits. Specimens of P. cathybrownae provide
critical floral characters previously unknown from the fossil
record that place these flowers confidently with the genus and
thereby provide a point of reference for its diversification.
A second rosaceous fossil flower from Republic demon-
strates the characteristic features of the monotypic Oemleria
cerasiformis (Torr. & A. Gray) Landon known as the oso-
berry or flowering plum (Stein 2008). Oemleria janhartfor-
dae Benedict, DeVore, & Pigg, sp. nov. (Rosaceae: subfamily
Spiraeoideae, tribe Osmaronieae sensu Potter et al. 2007) is
described from a single distinctive flower with five free car-
pels that each have characters similar to Prunus, including
a flattened bilobed stigma; elongate laterally fixed style; and
an ellipsoid, bilaterally asymmetric ovary. Today this mono-
specific genus is endemic to the Pacific Northwest, with a range
from northern California to southwestern British Columbia
(Pojar and MacKinnon 2004; Stein 2008). These fossils pro-
vide the first evidence of diagnostic floral characters that
clearly demonstrate that these two genera were present in the
latest early Eocene of western North America. They doc-
ument further details of mode and tempo of the diversification
of the Rosaceae, an important mostly temperate, mostly North-
ern Hemisphere family (Hutchinson 1964; Heywood 1993).
Material and Methods
Fossil flowers are preserved as coalified compressions in
the Republic flora of Republic (Ferry Co.), northeastern
Washington State, United States, where they occur in a light
gray lacustrine shale. All Prunus specimens and the Oemleria
flower were collected from the Boot Hill locality, a site where
both researchers and the public have collected steadily for
more than 20 yr. The fossiliferous horizon occurs within the
Tom Thumb Member of the Klondike Mountain Formation.
Dating by
40
Ar-
39
Ar dating listed in an abstract by Wolfe
et al. (2003) gives an age of 49:42 6 0:54 Ma, which is con-
sidered late early Eocene (see Greenwood et al. 2005).
Flower and fruit specimens were photographed with LM.
Fragments of anthers from both the inner and the outer
whorls of the holotype ower R2 (SR 96-11-47AB) were re-
moved. Anther fragments from the inner whorl yielded clumps
containing many very small grains. These were coated with
;20 nm of gold coating, mounted on stubs, and viewed on
a Leica-Cambridge (Structure Probe, Westchester, PA) stereo-
scan 360FE SEM at 10 kV. Anthers from the outer whorl
contained fewer, larger pollen grains that were treated with
hydrofluoric acid and isolated by heavy liquid separation us-
ing zinc chloride. Extant specimens of Prunus flowers were
dissected and photographed with LM. Fossil specimens and
photographs are housed at the Stonerose Interpretive Center,
Republic, Washington, and extant comparative material is
housed in the Paleobotanical Collections, School of Life Sci-
ences, Arizona State University, Tempe.
Systematics of Prunus cathybrownae
Class—Magnoliopsida
Subclass—Rosidae
Order—Rosales
Family—Rosaceae Juss.
Subfamily—Spiraeoideae C. Agardh
Tribe—Amygdaleae Juss.
Genus—Prunus L.
Prunus Type Species—Prunus domestica Linn. B.H. 1:609
Species—Prunus cathybrownae Benedict,
DeVore, & Pigg, sp. nov.
Species diagnosis. Flowers with pedicels 3–8 (up to 15)
mm long (
X ¼ 6:15, n ¼ 10) 3 0.5–1.0 mm wide (X ¼ 0:7,
n ¼ 10); actinomorphic, perigynous, pentamerous; hypanthium
campanulate, 3–4 mm long (
X ¼ 3:2, n ¼ 7) 3 4–6 mm wide
(
X ¼ 4:29, n ¼ 7), length : width ratio 0.75 : 1, hypanthial rim
with inserted sepals and stamens; sepals five, 1 mm long
3 1
mm wide, ovate with pointed apical tip; gynoecium unicar-
pellate, stigma distally flared, 0.5–1 mm wide, bilobed; style
elongate, 1–4 mm long
3 0.5–1.0 mm wide; ovary 1.5–3.0
949
BENEDICT ET AL.—FOSSIL PRUNUS FLOWERS
long (X ¼ 2:6, n ¼ 6) 3 1–2 mm wide (X ¼ 1:83, n ¼ 6), el-
lipsoid, bilaterally asymmetric; produced in two whorls, in-
ner whorl reflexed, outer whorl extended; anthers dorsifixed;
mature pollen tricolporate, striate, 20 mm in diameter; imma-
ture fruits 4.5–5.0 mm long
3 3.0–3.5 mm wide with par-
tially symmetrical ellipsoid ovary.
Previous illustrations. DeVore and Pigg 2007, figures 1–4.
Type locality. Boot Hill (University of Washington Burke
Museum of Natural History and Culture locality B4131), Re-
public, Ferry County, Washington.
Stratigraphy. Late early Eocene, Tom Thumb Member of the
Klondike Mountain Formation; 49:42 6 0:54 Ma on the basis
of
40
Ar -
39
Ar dating (Wolfe et al. 2003; Greenwood et al. 2005).
Holotype. R2, SR 96-11-47AB (figs. 1A,3D,5A,5C
5G), collected by a Stonerose staff member, housed at Stone-
rose Interpretive Center, Republic, Washington.
Paratypes. Specimen and Stonerose collection number,
followed by collector: R1, SR 05-05-06AB, A. H. Smith (figs.
1D,2C,2D,3B,3C); R7, SR 05-05-03, C. Backman (fig.
1G); R12, SR 96-09-09, D. Gibson (fig. 1I); R40, SR 08-06-
06AB, J. Shafer (figs. 1C,2E,3E); R41, SR 08-40-21AB, D.
Marino and E. Bensing, (fig. 1F); R42, SR 09-09-25AB, M.
Stevens (figs. 1K,3H); R43, SR 09-09-12AB, C. Middleton
(figs. 1J,3G); R45, SR 09-09-19AB, J. Armstrong (not fig-
ured); and R60, SR 08-42-02AB, M. Jones (figs. 1E,2A,2F,
3F,3I). All paratypes are housed at Stonerose Interpretive
Center, Republic, Washington.
Etymology. The species epithet cathybrownae is named
in honor of three generations who bear this name: Catherine
Louise Brown, Director of Stonerose Interpretive Center, Re-
public; her mother, Catherine Evelyn Brown, Republic, artist
and enthusiastic supporter of Stonerose; and her daughter,
Catherine Clementine Brown, special assistant at Stonerose.
We honor their extraordinary dedication to the curation and
study of Republic fossils through Stonerose Interpretive Cen-
ter and its mission of community and educational outreach.
Description
The description is based on 10 laterally compressed speci-
mens, eight of which are part-counterparts, while the remain-
ing two are individuals. Eight of these are mature flowers
with features remarkably similar to those of extant Prunus
(fig. 1A–1I); two are immature fruits (fig. 1J,1K ). Flowers
are actinomorphic, perigynous, and pentamerous and are char-
acterized by a campanulate hypanthium (figs. 1C,1F,1G,
2A,2E). Sepals and stamens are inserted along the apex of
the hypanthial rim (fig. 2A,2C–2F). The gynoecium is uni-
carpellate with a distally flared, bilobed stigma; elongate
style; and an ellipsoid, bilaterally asymmetric ovary (fig. 3B).
All specimens are pedicellate, with the pedicel ranging
from 3 to 8 mm long (
X ¼ 6:15, n ¼ 10) 3 0.5–1.0 mm wide
(
X ¼ 0:7, n ¼ 10), but are incomplete, and their entire
lengths are unknown (fig. 1C,1E,1F). One small flower (fig.
1G) has a pedicel 15 mm long
3 1.0 mm wide. The campan-
ulate hypanthium is 3–4 mm high and 4–6 mm across, with
a length : width ratio of 0.75 : 1, and extends around the
base of the gynoecium. In some specimens it is well preserved
(figs. 1A,1C,1E–1G,2A,2E), while in others only remnants
remain (figs. 1D,1I,2C,2D). Sepals preserved in a few
flowers are 1 mm long
3 1 mm wide and broadly ovate, with
a pointed apical tip (fig. 2A,2F). Although petals of various
types are known in the Republic matrix, none have been
found in attachment to P. cathybrownae flowers, suggesting
that, as in extant Prunus, they fell off postanthesis.
At the apical end of the gynoecium, the stigma is bilobed
and up to 1.0 mm wide (fig. 3C–3E). It extends into an elon-
gate style (figs. 1A,1D–1G,2D,3B) that is typically 1–4
mm long (
X ¼ 2:6, n ¼ 7) 3 0.2–1.0 mm wide (X ¼ 0:5,
n ¼ 6), for a length : width ratio of 6.4 : 1. In one specimen,
the style is notably shorter and thicker, measuring 2.0 mm
long
3 0.8 mm wide (fig. 1C). In the flower specimens (figs.
1A,1C–1E,1G,1I,3B), the ovary is 1.5–3.0 mm long
(
X ¼ 2:6, n ¼ 6) 3 1–2 mm wide (X ¼ 1:8, n ¼ 6).
Two specimens are of immature fruits. In contrast to the
flowers, each has a larger and more symmetric ovary and
fewer perianth parts. The ovary is 4.5 mm long
3 3.0 mm
wide in one fruit (figs. 1J,3F,4D) and 5.0 mm long
3 3.5 mm
wide in the other (fig. 1K). One shows the remnant of a style
at the apex (figs. 1J,3F,4D), while in the other the style is
lacking (figs. 1K,3G).
The androecium is characterized by around a dozen sta-
mens borne in two whorls. In the outer whorl, stamens have
filaments ;6 mm long extending apically above the gynoe-
cium (figs. 1A,1D–1F,2A,2C,2D,5A). In the inner whorl,
stamens are reflexed and extend to the level of the style base.
Some stamens of the inner whorl are arranged loosely to one
another along the hypanthial rim, such that they superficially
appear to be branched (figs. 1D,2C), as in extant Prunus (figs.
1H,2B). Anthers are 0.5 mm wide and dorsifixed (fig. 5A,5C,
5F) and are similar to those of extant Prunus (fig. 5B).
Two types of pollen have been found within the flowers.
Clusters of small grains 7 mm long and 4 mm wide are found
in the anthers of the inner whorl of reflexed stamens (fig. 5D,
5E). These grains have an exine with poorly defined ornamen-
tation (fig. 5E). Mature rosaceous pollen was recovered from
an anther of the outer whorl of stamens. As seen in LM, these
grains are 20 mm in diameter and tricolporate, with a striate
ornamentation with lumina around 1 mmacross(g.5G–5H).
Systematics of Oemleria janhartfordae
Class—Magnoliopsida
Subclass—Rosidae
Order—Rosales
Family—Rosaceae
Subfamily—Spiraeoideae C. Agardh.
Tribe—Osmaronieae Rydb.
Genus—Oemleria Reichenb.
Type Species—Oemleria cerasiformis (Torr. &
A. Gray ex Hook. & Arn.) Landon
Species—Oemleria janhartfordae Benedict,
DeVore, & Pigg, sp. nov.
Species diagnosis. Flower bractate, pedicellate, pedicel 11
mm long
3 1 mm wide; actinomorphic, perigynous; gynoecium
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INTERNATIONAL JOURNAL OF PLANT SCIENCES
Fig. 1 Fossil Prunus cathybrownae sp. nov. (A, CG, IK) and extant Prunus cerasus (B, H) for comparison. A, Holotype specimen. R2, SR
96-11-47A. B, Extant P. cerasus flower cut in longitudinal section. C, Flower with short, stout style and campanulate hypanthium. R40, SR 08-06-
06A. D, Flower showing a campanulate hypanthium with attached stamens. R41, SR 08-40-21A. E, Flower with well-preserved gynoecium,
sepals, and filaments. R60, SR 08-42-02A. F, Flower with gynoecium, hypanthium, and attached perianth parts. R1, SR 05-05-06B. G, Small
flower with long pedicel. R12, SR 05-05-03. H, Extant flower for comparison. Hypanthium has been removed from front of specimen. I, Flower
with flared stigma, bent style, and remnants of perianth. R7, SR 96-09-04. J, Immature fruit. Note remnant of style (arrow). R43, SR 09-09-12A.
K, Immature fruit lacking style. R42, SR 09-09-25B. Scale bars ¼ 3 mm.
11 mm long 3 6 mm wide; pistils 5, free, each with a flattened,
bilobed stigma, style laterally fixed, elongate, 3 mm long
3 1
mm wide; ovary 5 mm long
3 3 mm wide, ellipsoid, bilaterally
asymmetric; hypanthium surrounding base of the five carpels.
Type locality. Boot Hill (University of Washington Burke
Museum of Natural History and Culture locality B4131), Re-
public, Ferry County, Washington.
Stratigraphy. Late early Eocene, Tom Thumb Member of
the Klondike Mountain Formation; 49:42 6 0:54 Ma based on
40
Ar -
39
Ar dating (Wolfe et al. 2003; Greenwood et al. 2005).
Holotype. R47, SR 08-42-15AB (fig. 6A,6C–6F), col-
lected by Stonerose staff, 2006; housed at Stonerose Interpre-
tive Center, Republic, Washington.
Etymology. The species epithet, janhartfordae, honors
Jan Hartford of Republic, Washington, for her exceptional
dedication to the collecting and study of the Republic flora
and for developing the customized database Stonerose Strata,
an innovative program that is essential to the workings of
Stonerose Interpretive Center.
Description
Oemleria janhartfordae is based on a single part-counterpart
flower specimen (fig. 6A,6C–6F) and is quite similar to extant
Oemleria (fig. 6B,6G). The actinomorphic, perigynous flower
is fractured longitudinally, and its gynoecium is 11 mm long
3
6 mm wide. It is borne on a pedicel 11 mm long 3 1mmwide.
On the pedicel, an abscission scar is evident, which shows that
the flower was subtended by at least one bract (fig. 6A). The
flower has five free pistils that are basally inserted on the pedi-
cel (fig. 6A,6C,6D,6F). Each bilaterally asymmetric ovary is
around5mmlong
3 3 mm wide, with a flattened bilobed
stigma 1 mm wide and an elongate style 3 mm long
3 0.5 mm
wide that is attached laterally to the ovary (fig. 6E,6F). The
five pistils are surrounded by an incompletely preserved hypan-
thium that covers the bottom half of the ovary wall. Androecia
and petals are lacking; the flower is presumably postanthesis.
General Discussion
Identification of Republic Flowers
The fossil flowers described in this report were identified to
modern Prunus and Oemleria on the basis of highly character-
istic floral features of these two genera. These fossils have flo-
ral structures that are consistent with not only those of the
modern genera but also ones that are used, essentially, to iden-
tify the extant forms. In the case of Prunus, these features in-
clude the bilobed stigma, elongate style and asymmetric ovary,
and the characteristic hypanthium (cf. fig. 1A,1B,1E;fig.2A,
2B;fig.3A,3B). Oemleria is characterized by five free pistils
that each individually resemble a single Prunus pistil (cf. fig.
6A,6G;fig.6B,6C). In contrast, other rosaceous taxa in the
Okanogan Highlands appear to have mosaic features of mod-
ern forms (e.g., Spiraea-like leaves) or to be completely extinct
(e.g., Stonebergia; DeVore and Pigg 2007).
In the most commonly recognized traditional classifications,
Prunus and related genera are placed within Prunoideae sensu
Fig. 2 Fossil Prunus cathybrownae sp. nov. (A, CF) and extant Prunus cerasus (B) for comparison. A, Flower with sepals and stamens
attached to hypanthium. R60, SR 08-42-02A. B, Extant P. cerasus flower for comparison. C, Flower with remnants of hypanthium at arrows. R1,
SR 05-05-06A. D, Hypanthium and stamen attachment. R1, SR 05-05-06B. E, Flower with well-preserved campanulate hypanthium. R40, SR 08-
06-06A. F, Detail of A showing sepals. R60, SR 08-42-02A. Scale bars ¼ 2mm(AC, E), 1 mm (D, F).
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INTERNATIONAL JOURNAL OF PLANT SCIENCES
Rehder (¼Amygdaloideae sensu Takhtajan) on the basis of
their fruit type, the drupe (Rehder 1940; Takhtajan 1997).
Within this subfamily, there has been considerable variation in
both number of taxa and taxonomic levels recognized. Up to
around a dozen genera have been created by some authors,
while others acknowledge a large genus, Prunus, along with
several smaller genera, such as Maddenia, Prinsepia, Exochorda,
and Oemleria (Takhtajan 1997; Potter et al. 2007).
Characters uniting the traditional subfamily include white
to pink flowers; a solitary, umbellate, or racemose inflores-
cence; 10 to many stamens; free carpels; an ovary with two
ovules that develops into a drupe with one or, rarely, two
seeds; and typically a stony endocarp (Rehder 1940). Prunus
and its segregate genera are unipistillate, with the exception
of Oemleria and Exchorda, which have five free pistils. Petals
and sepals are typically present, unique, and five in number,
with the exception of Maddenia, which has 10 tepals (Chin
et al. 2010). Prinsepia can be distinguished from the other
unipistillate genera by its lateral style (Rehder 1940).
Phylogenies based on recent molecular studies differ consid-
erably from traditional classifications throughout the Rosaceae
(Kalkman 1988, 2004; Potter et al. 2007). In many cases, the
traditional taxonomic units have been collapsed into larger
groups. For example, Maddenia, once considered a distinctive
genus on the basis of a uni- or bicarpellate gynoecium and 10
tepals, is now recognized as a member of Prunus and a part of
the Laurocerasus-Padus clade (Lee and Wen 2001; Bortiri
et al. 2006; Wen et al. 2008; for a discussion and taxonomic
revisions, see Chin et al. 2010). Whereas the traditional classi-
fication relied heavily on inflorescence type, this character was
not diagnostic of newly recognized clades (e.g., subgenera
Laurocerasus and Padus, as described by Rehder 1940).
Prunus cathybrownae
Prunus cathybrownae conforms to Prunus on the basis of
the following characters: a campanulate hypanthium, a single
free carpel, five sepals, and at least a dozen stamens. Pistils
Fig. 3 Fossil Prunus cathybrownae sp. nov. (BI) and extant Prunus cerasus (A) for comparison. A, Extant gynoecium with flattened, bilobed
stigma and elongate style. B, Gynoecium showing typical flattened, bilobed stigma; elongate style; and elliptical, bilaterally asymmetric ovary. R1,
SR 05-05-06B. C, Detail of B showing stigma in lateral view showing bilobed shape. R1, SR 05-05-06B. D, Detail of holotype specimen showing
lateral view of stigma. R2, SR 96-11-47A. E, Detail of fig. 1C showing top view of stigma with bilobed shape. R40, SR 08-06-06B. F, Ovary with
preserved cellular detail. R60, SR 08-42-02A. G, Immature fruit showing remnant of style (arrow) and ovoid symmetric ovary. R43, SR 09-09-
12A. H, Immature fruit. R42, SR 09-09-25B. I, Detail of F showing surface of ovary wall. R60, SR 08-42-02A. Scale bars ¼ 2mm(A, B), 1 mm
(CF), 3 mm (G, H), 0.25 mm (I).
953
BENEDICT ET AL.—FOSSIL PRUNUS FLOWERS
are strikingly similar to those of extant Prunus in their mor-
phological features, most notably the flattened, bilobed stigma;
elongate style; and ellipsoid, bilaterally asymmetric ovary.
On the basis of this characteristic shape of the ovary, it can
be inferred that, as in extant Prunus, P. cathybrownae pre-
sumably produced two ovules, only one of which would de-
velop into a mature seed (Sterling 1953).
All of the eight flower specimens of P. cathybrownae are
interpreted as being at postanthesis on the basis of the lack
of petals; stamens that usually lack intact anthers; and the
slightly swollen, bilaterally asymmetric ovary. In addition to
size differences, variation in morphology suggests that several
stages are present. Whereas most of the specimens have an
upright style (fig. 1A,1C–1G), in one the style is bent, sug-
gesting the beginning of floral senescence, as seen in extant
Prunus (fig. 1I,1H). The formation of an abscission scar be-
neath the ovary as well as the absence of hypanthia in imma-
ture fruits suggests that the hypanthium was deciduous (fig.
1J,1K). Together the flower and the two individual fruit speci-
mens are consistent in size with the rate of enlargement ob-
served in extant Prunus flowers and young fruits from full
bloom through early fruit initiation (Tukey and Young 1939).
Features of the stamens also present details of several
stages of floral development. One specimen demonstrates an
inner whorl of reflexed stamens and an outer one of upright
stamens, as noted in extant Prunus flowers (Evans and Dick-
inson 1999). The clusters of smaller pollen grains recovered
from the inner whorl are interpreted as immature grains.
Whether the exine ornamentation is lacking because of poor
preservation or is simply not yet present at this developmen-
tal stage is unknown, but a similar situation was found in
anatomically preserved flowers of Wehrwolfea allenbyensis
(Sapindaceae), known from the contemporaneous Princeton
chert (Erwin and Stockey 1990). The mature pollen found in
the outer whorl of anthers in P. cathybrownae is tricolporate
and has striate ornamentation typical of extant Prunus pollen
(fig. 5G,5H). This pollen falls within a size range of pollen
known from extant Prunus, which can vary from tricolpate
to tricolporate (Hebda and Chinnappa 1990).
A recent study of character evolution within Prunus as-
sessed the distribution of 25 morphological characters (Bortiri
et al. 2006). Seven of these characters that refer to floral
features can be compared with P. cathybrownae. Prunus
cathybrownae is unicarpellate, with a deciduous, campanulate
hypanthium. Sepals are less than half the length of the hypan-
thium. The calyx lobe margin is entire and lacks evidence of
a well-developed indument. Flowers are small and, on the ba-
sis of one specimen with an elongate pedicel, suggest that the
pedicel may have been longer than the fruit. At the least, fruits
are not sessile. A comparison of the features of P. cathybrow-
nae with the Bortiri et al. (2006) study shows that it has a com-
bination of morphological characters representative of extant
species that occupy basal positions in the genus. At the current
time, it is difficult to resolve the position of P. cathybrownae
within extant Prunus because many of the traditional charac-
ters used to classify subgenera and species have been found to
be homoplastic (Shaw and Small 2004; Bortiri et al. 2006).
Prunus leaves are also a relatively common component of
the Republic flora (DeVore and Pigg 2007). Many are elliptic
with a thin lamina and serrate margins with small, regular
teeth, and they presumably were deciduous. These features are
considered basal in the genus (Bortiri et al. 2006). The exact
placement of P. cathybrownae
within the genus Prunus cannot
be determined; however, this combination of features seen in
the flowers and associated leaves is consistent with the Repub-
lic form(s) of Prunus occupying a basal position in the genus.
In addition to the fossil flowers, young fruits, and leaves of
Prunus from Republic, remains of the genus are known from
several other Eocene localities in western North America.
Anatomically preserved endocarps have been described from
the Princeton chert. These fruits are based on only a few
specimens and were informally designated as types 1, 2, and
3 (Cevallos-Ferriz and Stockey 1991). They have the typical
morphology and anatomical structure of Prunus fruits with
variable distributions of sclereids and fibers, and they have
similarities with the endocarps of the subgenera Prunus
Koehne and Euprunus Koehne (Mai 1984; Cevallos-Ferriz
Fig. 4 Line diagram showing gynoecia from several different
developmental stages. A, Small flower illustrated in fig. 1G. Redrawn
from R7, SR96-09-04. B, Flower in fig. 1D. Redrawn from R1, SR 05-
05-06A. C, Flower in fig. 1I. Redrawn from R12. D, Immature fruit in
fig. 1J. Redrawn from R43, SR 09-09-12A. Scale bar ¼ 5 mm.
954
INTERNATIONAL JOURNAL OF PLANT SCIENCES
and Stockey 1991). Cevallos-Ferriz and Stockey (1991) com-
mented that it was difficult to demonstrate conclusively the
relationships of the fossil endocarps to extant ones because
specimens lacked some informative characters and because of
the limited knowledge of variability among extant forms.
Two species were described from the Clarno Nut Beds of
Oregon (Manchester 1994), one of which, Prunus weinsteinii
Manchester, was compared closely with type A from Prince-
ton. The other species, Prunus olsoni Manchester, is similar
to extant Prunus avicina (Manchester 1994). Prunus endo-
carps are also well represented in the fruit and seed floras of
Europe from the Eoceneon, with fossils representing at least
five subgenera of Prunus (Kirchheimer 1973; Mai 1984). To
date, we have not identified Prunus endocarps from Repub-
lic. Woody twigs from the Princeton chert (Cevallos-Ferriz
and Stockey 1990) and specimens representing the remains
of larger trees at Clarno and Yellowstone (Wheeler et al.
1978; Wheeler and Manchester 2002) show the characteristic
features of Prunus wood, including traumatic resin ducts.
Oemleria janhartfordae
In addition to reporting the first occurrence of Prunus
flowers in the Tertiary, we now also recognize the first reli-
able evidence of Oemleria floral remains at Republic. To our
knowledge, the only other fossil report of the genus (under
Fig. 5 Fossil Prunus cathybrownae sp. nov. (A, CH), all from the holotype specimen (fig. 1A; SR 96-11-47A&B), and extant Prunus cerasus
(B) and extant Prunus dulcis (H) for comparison. A, Androecium surrounding pistil. B, Extant flower showing dorsifixed anthers arranged toward
the gynoecium. C, Dorsifixed anther from outer whorl of stamens. D, SEM of mass of immature pollen from anther of inner whorl. E, Detail of
immature pollen grain. F, Stamen from inner whorl with dorsifixed anther recurving toward the gynoecium G, Pollen from anther of external
whorl. H, Extant pollen for comparison. Scale bars ¼ 2mm(A, B), 1 mm (C , F), 12 mm(D), 3 mm(E), 20 mm(G), 30 mm(H).
955
BENEDICT ET AL.—FOSSIL PRUNUS FLOWERS
Fig. 6 Oemleria janhartfordae sp. nov. flower (A, CF) and extant Oemleria cerasiformis for comparison (B, G). A, Overview of flower with
attached pedicel. Inset, detail of pedicel showing bract scar. R47, SR 08-42-15A. B, Extant O. cerasiformis for comparison. C, Detail of A showing
two of the five pistils (arrows). D, Counterpart of A. R47, SR 08-42-15B. E, Detail of bilobed stigma from D. F, Detail of a single pistil from A
showing lateral style. G, Extant O. cerasiformis flower postanthesis showing separate pistils, line of hypanthial dehiscence, and subtending floral
bracts. B and G courtesy of G. D. Carr. Scale bars ¼ 5mm(AD, G), 1 mm (inset in A, E, F).
its inv alid gener ic name, Osmaronia) was described ten-
tatively from a leaf compression in late Oligocene Creede
flora of Colorado as Osmaronia? stewartiae (Landon 1975;
Axelrod 1987; Schorn and Wolfe 1989). Today Oemleria is
a monotypic genus endemic to western North America, with
a range from the Pacific Coast to the Cascades from northern
California to southwestern British Columbia (Stein 2008).
Plants are dioecious and grow in alluvial or moist soil. It has
been reported that this genus is restricted to a maritime cli-
mate (Antose and Allen 1990; Stein 2008).
The occurrence of fossil Oemleria in the Republic flora pro-
vides evidence for its early presence in the Northwest. The
geographic distribution of extant Oemleria has been intriguing
to botanists interested in endemic genera. For example, Little
(1971–1981), who compiled species distribution maps for the
trees of North America, hypothesized that endemic forms
were either (1) relicts of older genera that once had a wider
range or (2) young genera that lacked a fossil record. Of the
eight genera he recognized from coastal and subtropical zones
of California, five belong to Rosaceae. Oemleria was of partic-
ular interest. Little (1983) speculated that Oemleria originated
from Prunus, lacked a fossil record, and therefore must be
‘young.’ With this report, we can now establish the presence
of fossil flowers belonging to Oemleria co-occuring with those
of Prunus in the latest early Eocene.
Biogeographic Occurrences of Supertribe
Kerriodae (Rosaceae)
In the current classification of Rosaceae (Potter et al.
2007), supertribe Kerriodae comprises two tribes, Osmaro-
nieae and Kerrieae. Both of these tribes have fossil repre-
sentatives at Republic, Oemleria and t he genus Ne viusi a ,
previously described fro m One Mile Creek, British Co lum-
bia, and now also known from Republic (DeVore et al.
2004). Oemleria is distributed today on the West Coast of
North America, while the other two genera in tribe Osmaro-
nieae, Exochorda and Prinsepia, are Asian. Kerrieae also has
a North American–Asian disjunct distribution today, with
Kerria and Rhodotypus in Asia, Coloeogyne widespread in
the American Southwest, and Neviusia disjunct between east-
ern and western North America (Shevock et al. 1992; DeVore
et al. 2004). These newly described fossils plus previously
known fossils from Republic and other Okanogan Highlands
sites underscore the significance of this region as a center of
rosaceous diversification in the Eocene.
Acknowledgments
We thank Catherine L. Brown and Karl E. Volkman, Stone-
rose Interpretive Center, for loaning us the specimens for
study; Nathan D. Wilkens for technical assistance; Wes Wehr
for identifying many of the specimens; Marilyn B. Canteloupe
for providing extant material of Prunus cerasus;GeraldD.
Carr for providing images of Oemleria cerasiformis; and the
School of Life Sciences, Arizona State University, for SEM
facilities. Jane Maienschein and the Center for Biology and
Society, Arizona State University, provided travel funds. We
dedicate this article to the late Maria Tcheropova, who ini-
tially recognized the resemblance of these Republic flowers to
those of modern Prunus.
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... The fossil record of Moraceae is comparatively poor and in need of critical revision (Collinson 1989), whereas unambiguous fossils exist for other families of Rosales (Burge and Manchester 2008;Benedict et al. 2011;Friis et al. 2011). When reliable fossils are absent or scarce for the ingroup, outgroup calibration may provide more accurate estimates than secondary calibration (Sauquet et al. 2012;Hipsley and Müller 2014). ...
... To revise fossil calibrations in Rosales, we proceeded as follows (Parham et al. 2012;Sauquet et al. 2012): 1) we started from lists of calibrations used in previous molecular dating studies (Zerega et al. 2005;Cruaud et al. 2012;Magallón et al. 2015) and completed this list with specific reviews (Collinson 1989;Friis et al. 2011) and recently published fossil taxa (Manchester 1999;Calvillo-Canadell and Cevallos-Ferriz 2007;Manos et al. 2007;Benedict et al. 2011); 2) for each fossil, we critically assessed the phylogenetic assignment based on original descriptions and subsequent reviews, and using the latest reference phylogeny for each family (Manchester 1999;Calvillo-Canadell and Cevallos-Ferriz 2007;Manos et al. 2007;Benedict et al. 2011;Friis et al. 2011;Jud et al. 2017); 3) ...
... To revise fossil calibrations in Rosales, we proceeded as follows (Parham et al. 2012;Sauquet et al. 2012): 1) we started from lists of calibrations used in previous molecular dating studies (Zerega et al. 2005;Cruaud et al. 2012;Magallón et al. 2015) and completed this list with specific reviews (Collinson 1989;Friis et al. 2011) and recently published fossil taxa (Manchester 1999;Calvillo-Canadell and Cevallos-Ferriz 2007;Manos et al. 2007;Benedict et al. 2011); 2) for each fossil, we critically assessed the phylogenetic assignment based on original descriptions and subsequent reviews, and using the latest reference phylogeny for each family (Manchester 1999;Calvillo-Canadell and Cevallos-Ferriz 2007;Manos et al. 2007;Benedict et al. 2011;Friis et al. 2011;Jud et al. 2017); 3) ...
Thesis
Angiosperms are the most diversified clade of extant plants and are exceptionally species-rich in tropical regions. In this thesis, I investigated breeding system evolution and biogeographic history in the family Moraceae, which I used as a model clade to understand the origin and evolution of diversity of angiosperms. In Chapter I, I reconstructed and calibrated a new dated phylogenetic tree for Moraceae as a whole. I then used this tree to reconstruct ancestral states of breeding systems in Moraceae and Ficus. The crown group ages of Moraceae and Ficus were estimated in the Cretaceous and in the Eocene, respectively. Dioecy was inferred as the ancestral breeding systems of Moraceae, with several subsequent transitions to monoecy, including in Ficus. This result suggests that dioecy is not necessarily an evolutionary dead end. In Chapter II, I reconstructed a dated phylogenetic tree for tribe Dorstenieae, mainly distributed in tropical regions, with a new data set of nuclear genomic data generated with a Hyb-Seq approach. Biogeographic history was then reconstructed using dispersal-extinction-cladogenesis models. The crown group ages of Dorstenieae and Dorstenia were estimated in the Cretaceous and in the Cretaceous/Paleocene period, respectively. Two long-distance dispersal events from continental Africa to South America occurred in the Cenozoic (Dorstenia and Brosimum s.l.). In Chapter III, I tested the climatic niche difference (temperature and precipitation) between the two breeding systems (monoecy and gynodioecy) in Ficus using a new dataset of cleaned spatial occurrence records and breeding systems for 183 species. I used two comparative approaches: generalized estimating equations (GEE) and generalized linear models (GLM). A positive relationship between precipitation and gynodioecy was supported by GLM, but not GEE analyses, and no relationship between temperature and breeding systems was supported by either method. Higher dispersal ability and the potential for self-fertilization may explain why monoecious species of Ficus have been able to colonize and survive in drier environments. This thesis highlights the potential of phylogenetic comparative methods and phylogenomic data to address questions of breeding system evolution and biogeography in Moraceae, and opens up several important new perspectives worth investigating in other plant clades, such as a relationship between breeding system and climatic niche.
... The fossil record of Moraceae is comparatively poor and in need of critical revision (Collinson, 1989), whereas unam- biguous fossils exist for other families of Rosales ( Burge and Manchester, 2008;Benedict et al., 2011;Friis et al., 2011). When reliable fossils are absent or scarce for the ingroup, outgroup calibration may provide more accurate estimates than secondary calibration (Sauquet et al., 2012;Hipsley and Müller, 2014). ...
... Our set of fos- sil age constraints includes four in Moraceae and eight distrib- uted among the remaining families of Rosales (Supplementary Data Table S2). To revise fossil calibrations in Rosales, we proceeded as follows (Parham et al., 2012;Sauquet et al., 2012): (1) we started from lists of calibrations used in previ- ous molecular dating studies (Zerega et al., 2005;Cruaud et al., 2012;Magallón et al., 2015) and completed this list with spe- cific reviews (Collinson, 1989;Friis et al., 2011) and recently published fossil taxa (Manchester, 1999;Calvillo-Canadell and Cevallos-Ferriz, 2007;Manos et al., 2007;Benedict et al., 2011); (2) for each fossil, we critically assessed the phylogen- etic assignment based on original descriptions and subsequent reviews, and using the latest reference phylogeny for each fam- ily (Manchester, 1999;Calvillo-Canadell and Cevallos-Ferriz, 2007;Manos et al., 2007;Benedict et al., 2011;Friis et al., 2011;Jud et al., 2017); (3) for each fossil, we also critically revised the absolute age or age range of the fossil using the lat- est stratigraphy and geological time scale from the International Commission on Stratigraphy (Cohen et al., 2017). Because none of these fossil taxa has been included in total evidence phylogenetic analyses, our assignments here are at best 'apo- morphy based' and therefore we have been particularly con- servative in both selecting our final calibrations and assigning them to clades. ...
... Our set of fos- sil age constraints includes four in Moraceae and eight distrib- uted among the remaining families of Rosales (Supplementary Data Table S2). To revise fossil calibrations in Rosales, we proceeded as follows (Parham et al., 2012;Sauquet et al., 2012): (1) we started from lists of calibrations used in previ- ous molecular dating studies (Zerega et al., 2005;Cruaud et al., 2012;Magallón et al., 2015) and completed this list with spe- cific reviews (Collinson, 1989;Friis et al., 2011) and recently published fossil taxa (Manchester, 1999;Calvillo-Canadell and Cevallos-Ferriz, 2007;Manos et al., 2007;Benedict et al., 2011); (2) for each fossil, we critically assessed the phylogen- etic assignment based on original descriptions and subsequent reviews, and using the latest reference phylogeny for each fam- ily (Manchester, 1999;Calvillo-Canadell and Cevallos-Ferriz, 2007;Manos et al., 2007;Benedict et al., 2011;Friis et al., 2011;Jud et al., 2017); (3) for each fossil, we also critically revised the absolute age or age range of the fossil using the lat- est stratigraphy and geological time scale from the International Commission on Stratigraphy (Cohen et al., 2017). Because none of these fossil taxa has been included in total evidence phylogenetic analyses, our assignments here are at best 'apo- morphy based' and therefore we have been particularly con- servative in both selecting our final calibrations and assigning them to clades. ...
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Background and aims: Although dioecy, which characterizes only 6 % of angiosperm species, has been considered an evolutionary dead end, recent studies have demonstrated that this is not necessarily the case. Moraceae (40 genera, 1100 spp., including Ficus, 750 spp.) are particularly diverse in breeding systems (including monoecy, gynodioecy, androdioecy and dioecy) and thus represent a model clade to study macroevolution of dioecy. Methods: Ancestral breeding systems of Ficus and Moraceae were inferred. To do so, a new dated phylogenetic tree of Ficus and Moraceae was first reconstructed by combining a revised 12-fossil calibration set and a densely sampled molecular data set of eight markers and 320 species. Breeding system evolution was then reconstructed using both parsimony and model-based (maximum likelihood and Bayesian) approaches with this new time scale. Key results: The crown group ages of Ficus and Moraceae were estimated in the Eocene (40.6-55.9 Ma) and Late Cretaceous (73.2-84.7 Ma), respectively. Strong support was found for ancestral dioecy in Moraceae. Although the ancestral state of Ficus remained particularly sensitive to model selection, the results show that monoecy and gynodioecy evolved from dioecy in Moraceae, and suggest that gynodioecy probably evolved from monoecy in Ficus. Conclusions: Dioecy was found not to be an evolutionary dead end in Moraceae. This study provides a new time scale for the phylogeny and a new framework of breeding system evolution in Ficus and Moraceae.
... Divergence of the clade including Rosa L. and Fragaria L. was calibrated using fossil Rosa germerensis Edelman from North America (C3: 50 mya, Edelman, 1975). We calibrated the clade including Prinsepia, Oemleria and Exochorda using fossil Oemleria janhartfordae Benedict & al. from North America (C4: 50 mya, DeVore & Pigg, 2007;Benedict & al., 2011). The node of the Vauquelinia clade including Vauquelinia Corrêa ex Bonpl., Sorbus L., Pyrus L., Crataegus L., Photinia Lindl., and Pyracantha M.Roem. ...
... The conflict of divergence time calibration is common when different markers (e.g., Near & al., 2012) are adopted or different OTUs sampled (Heath & al., 2008). This estimation is also younger than the radiometric dating of 49.42 ± 0.54 myr (early Eocene) from the fossil phylogenetic relative Oemleria janhartfordae from North America (Benedict & al., 2011). However, the radiometric dating of fossil Oemleria janhartfordae was used as a calibration point for the tribe Exochordeae (Exochorda + Prinsepia + Oemleria) in the molecular dating of Rosaceae by Chin & al. (2014), , and Zhang & al. (2017), although the fossil was described as a member of Oemleria. ...
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To understand better the mechanisms underlying the disjunct distribution of plants between Taiwan and Himalaya‐southwestern China, the genus Prinsepia (Rosaceae) was examined using phylogenetic and dating approaches based on molecular evidence. Prinsepia comprises four allopatric species with distributions in four subregions of China, i.e., P. scandens (southeastern China: Taiwan), P. sinensis (northeastern China: Heilongjiang, Jilin, Liaoning and E Inner Mongolia), P. uniflora (mainly northwestern China: Gansu, Henan, W Inner Mongolia, Ningxia, Qinghai, Shaanxi, Shanxi and Sichuan), and P. utilis (southwestern China: Guizhou, Sichuan, Xizang, Yunnan). Our phylogeny and molecular dating suggest that Prinsepia diverged into northern and southern clades in the Oligocene (ca. 32.61 mya); subsequently, the northern species pair split around 16.25 mya, and P. scandens diverged from the Xizang population of P. utilis in 11.89 mya but migrated to Taiwan later. We integrated different lines of evidence including phylogeny, molecular dating, geological history, and niche modelling, and conclude that divergence between the northwestern and northeastern species was caused by environmental differentiation (i.e., humidity/aridity), and the modern disjunctive distribution of the southern species pair was better explained by founder speciation/migration. We thus provide new insights into the origin of the disjunction between Taiwan and Himalaya‐southwestern China.
... We used the original cpDNA sequences of all four species (without recoding and deleting two complex regions from psbA-trnH) to generate a haplotype file and these haplotypes were used for the divergence time estimation of cpDNA. The fossil records for Oemleria janhartfordae and Neviusia sp. from North America were used for calibration (DeVore et al., 2004;Benedict et al., 2011;Xiang et al., 2017). We used fossil constraint age, as provided by Xiang et al. (2017), and a standard deviation of 1.0 to calibrate the corresponding nodes. ...
... Oemleria is a monotypic genus endemic to western North America; this is the existing genus most closely related to Prinsepia (Xiang et al., 2017). Because the reliable fossil of Oemleria has been dated to late in the early Eocene epoch (49.42 ± 0.54 Ma) (Benedict et al., 2011), the origin time for Prinsepia should not follow after this time, if no other group had become extinct. All the related genera of Prinsepia, including Oemleria, Exochorda Lindl., Neviusia A. Gray, Kerria Candolle, Rhodotypos Siebold and Zuccarini, and Coleogyne Torrey, are all temperate taxa, which are distributed in East Asia or North America. ...
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Prinsepia Royle (Rosaceae) is a genus native to China and the Himalayan region. In order to explain its current fragmented distribution pattern and to compare the impact of relatively recent climate changes on the genetic structure of Prinsepia species in different regions of China, a total of 66 populations and 617 individuals of four species of Prinsepia were genotyped, using three cpDNA markers. Meanwhile, phylogenetic reconstructions and divergence dating were conducted using the cpDNA haplotypes dataset and the nuclear ribosomal internal transcribed spacer (ITS) dataset, respectively. Ecological niche modeling (ENM) was performed to predict the potential distribution of each species of Prinsepia at present and during the Last Glacial Maximum. Both ITS and cpDNA gene trees support a north-south divergence of Prinsepia species in China. The divergence time of the northern and southern Clades occurred around the late Oligocene epoch. Combining the present distribution of Prinsepia species and their habitats, we inferred that the transition to a monsoon climate system in East Asia during the late Oligocene epoch, created a humid forest vegetation zone from central to East China, which potentially gave rise to the north-south divergence of Prinsepia species. Both regional climates and allopatric divergence may have played an important role in the speciation of P. sinensis and P. uniflora. P. sinensis had the lowest genetic diversity and a putative northward post-glacial colonization. The distribution range of P. uniflora was also extremely sensitive to interglacial-glacial cycles. P. utilis from southwestern China preserved more haplotypes than P. sinensis and P. uniflora due to its multiple and isolated refugia.
... The analysis was based on 73 conserved chloroplast genes (51 protein-coding genes, 19 tRNAs, and 3 rRNAs) and allowed for four reliable fossil constraints (also used by Njuguna et al., 2013;Magallón et al., 2015), to be placed as primary calibration points along the tree (see Hohmann et al., 2015 for details on taxon sampling and data analysis). Namely, minimum ages of calibration points were the Prunus/Malus split set to 48.5 mya (Benedict et al., 2011), the Castanea/Cucumis split set to 84 mya (Sims et al., 1999), the Mangifera/Citrus split set to 65 mya (Knobloch and Mai, 1986) and the Oenothera/Eucalyptus split set to 88.2 mya (Takahashi et al., 1999). The root age of the tree was set to 92-125 mya (uniform distribution) in accordance with Magallón et al., 2015. ...
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With accelerating global warming, understanding the evolutionary dynamics of plant adaptation to environmental change is increasingly urgent. Here we reveal the enigmatic history of the genus Cochlearia (Brassicaceae), a Pleistocene relic that originated from a drought-adapted Mediterranean sister genus during the Miocene. Cochlearia rapidly diversified and adapted to circum-Arctic regions and other cold-characterized habitat types during the Pleistocene. This sudden change in ecological preferences was accompanied by a highly complex, reticulate polyploid evolution, which was apparently triggered by the impact of repeated Pleistocene glaciation cycles. Our results illustrate that two early diversified arctic-alpine diploid gene pools contributed differently to the evolution of this young polyploid genus now captured in a cold-adapted niche. Metabolomics revealed central carbon metabolism responses to cold in diverse species and ecotypes, likely due to continuous connections to cold habitats that may have facilitated widespread adaptation to alpine and subalpine habitats, and which we speculate were coopted from existing drought adaptations. Given the growing scientific interest in adaptive evolution of temperature-related traits, our results provide much-needed taxonomic and phylogenomic resolution of a model system as well as first insights into the origins of its adaptation to cold.
... This difference may be because chloroplast genes evolve slowly (Wolfe et al. 1987). In addition, we used a more ancient fossil, Prunus wutuensis (age: Early Eocene, 55.0 Ma), to calibrate the stem node of Prunus (Xiang et al. 2017) compared with Njuguna et al. (2013), who used Prunus cathybrownae (age: late Early Eocene, 48.4 Ma; Benedict et al. 2011). Although the 95% credibility interval from this study is largely overlapping with that estimated from transcriptomic data (Qiao et al. 2016), our estimate of the median age is slightly younger (i.e., compared with $7.99 Ma). ...
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The commercial strawberry, Fragaria × ananassa, is a recent allo-octoploid that is cultivated worldwide. However, other than F. vesca, which is universally accepted one of its diploid ancestors, its other early diploid progenitors remain unclear. Here, we performed comparative analyses of the genomes of five diploid strawberries, F. iinumae, F. vesca, F. nilgerrensis, F. nubicola, and F. viridis, of which the latter three are newly sequenced. We found that the genomes of these species share highly conserved gene content and gene order. Using an alignment-based approach, we show that F. iinumae and F. vesca are the diploid progenitors to the octoploid F. × ananassa, whereas the other three diploids that we analyzed in this study are not parental species. We generated a fully resolved, dated phylogeny of Fragaria and determined that the genus arose ca. 6.37 million years ago. Our results effectively resolve conflicting hypotheses regarding the putative diploid progenitors of the cultivated strawberry, establish a reliable backbone phylogeny for the genus, and provide genetic resources for molecular breeding.
... Flowers and inflorescences have important taxonomic value, and their developmental process contains abundant information for systematics and evolutionary studies (Endress 2011). Previous studies on Prunus have focused on its anatomy (Sterling 1953a(Sterling , 1953b(Sterling , 1964Haskell and Dow 1955;Endress and Stumpf 1991;Zhang 1992;Chin et al. 2013), palynology ( Hebda et al. 1991;Geraci et al. 2012; W.T. ), paleontology (DeVore and Pigg 2007;Benedict et al. 2011;Li et al. 2011), phylogenetics, and phylogeography ( Bortiri et al. 2002;Wen et al. 2008;Chin et al. 2010Chin et al. , 2014Liu et al. 2013;Zhao et al. 2016). Evans and Dickinson (1999a) compared the inflorescence and floral development of P. virginiana (subgenus Padus) with that of other Amygdaloid genera. ...
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Phylogenetic studies have shown that most clades in Prunus are well-supported by the flower structure, but most taxa in the racemose group have not yet been re-evaluated and could contribute to the understanding of the systematic relationships of the subgenera. We examined the inflorescence and flower development in Prunus laurocerasus L. (subgenus Laurocerasus) and P. serotina Ehrh. (subgenus Padus I) using scanning electron microscopy. Our results indicate that they share several floral development characters but differ in the following aspects: (i) all of their flowers are fully developed and each flower is enclosed by a bract and two bracteoles, which later stop development (vs. the terminal flower degenerates and only a single bract subtends each flower); (ii) the style protrudes from the floral bud (vs. the style is crooked and below the anthers); (iii) the outer integument initiates close to the inner one (vs. in the middle of the ovule); and (iv) an obturator appears after initiation of the two integuments (vs. simultaneously with the inner integument). Although our results are preliminary, differences in floral developmental characters support the different origins of Prunus subgenera Laurocerasus and Padus as based on molecular phylogenetic studies.
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The evolutionary histories of species have been shaped by genomic, environmental, and morphological variation. Understanding the interactions among these sources of variation is critical to infer accurately the biogeographic history of lineages. Here, using the geographically widely distributed plum genus (Prunus, Rosaceae) as a model, we investigate how changes in genomic and environmental variation drove the diversification of this group, and we quantify the morphological features that facilitated or resulted from diversification. We sequenced 610 nuclear loci and complete chloroplast genomes from 75 species representing all major lineages in Prunus, with a special focus on the understudied tropical racemose group. The environmental variation in extant species was quantified by synthesizing bioclimatic variables into principal components of environmental variation using thousands of georeferenced herbarium specimens. We used machine learning algorithms to classify and measure morphological variation present in thousands of digitized herbarium sheet images. Our phylogenomic and biogeographic analyses revealed that ancient hybridization and/or allopolyploidy spurred the initial rapid diversification of the genus in the early Eocene, with subsequent diversification in the north temperate zone, Neotropics, and Paleotropics. This diversification involved successful transitions between tropical and temperate biomes, an exceedingly rare event in woody plant lineages, accompanied by morphological changes in leaf and reproductive morphology. The machine learning approach detected morphological variation associated with ancient hybridization and quantified the breadth of morphospace occupied by major lineages within the genus. The paleotropical lineages of Prunus have diversified steadily since the late Eocene/early Oligocene, while the neotropical lineages diversified much later. Critically, both the tropical and temperate lineages have continued to diversify. We conclude that the genomic rearrangements created by reticulation deep in the phylogeny of Prunus may explain why this group has been more successful than other groups with tropical origins that currently persist only in either tropical or temperate regions, but not both.
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With accelerating global warming, understanding the evolutionary dynamics of plant adaptation to environmental change is increasingly urgent. Here we reveal the enigmatic history of the genus Cochlearia (Brassicaceae), a Pleistocene relic that originated from a drought-adapted Mediterranean sister genus during the Miocene. Cochlearia rapidly diversified and adapted to circum-Arctic regions and other cold-characterized habitat types during the Pleistocene. This rapid change in ecological preferences was accompanied by a highly complex, reticulate polyploid evolution, which was apparently triggered by the impact of repeated Pleistocene glaciation cycles. Our results illustrate that two early diversified arctic-alpine diploid gene pools contributed differently to the evolution of this young polyploid genus now captured in a cold-adapted niche. Metabolomics revealed ancestral central carbon metabolism responses to cold in diverse ecotypes, likely due to continuous connections to cold habitats that we hypothesize facilitated widespread parallel adaptation to alpine and subalpine habitats, and which we speculate were coopted from existing drought adaptations. Given the growing scientific interest in adaptive evolution of temperature-related traits, our results provide much-needed taxonomic and phylogenomic resolution of a model system as well as first insights into the origins of its adaptation to cold.
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The mid-Miocene Vantage Forest, conserved in the Ginkgo Petrified Forest State Park, Washington, U.S.A., is the single most diverse locality of Miocene woods in North America, with 34 angiosperm and 6 gymnosperm species. The composition of the Vantage forest is a mixture of plants now restricted to the eastern U.S. (e.g., hard elm group of Ulmus) and to Asia (Ginkgo), classic examples of disjunct genera (e.g., Liquidambar), and genera now widespread in the Northern Hemisphere (e.g., Quercus, Acer, Prunus). For many Vantage woods their relationships to extant taxa were evaluated in the context of recent phylogenetic work to see if there were wood anatomical features consistent with the groupings recovered in those studies and useful for determining which continent the closest living relatives inhabit. For Gleditsia such features were found. Ring porous and semi-ring porous woods are common in the Vantage assemblage, but there also are diffuse porous woods with relatively few wide vessels, a combination of features that today does not occur in temperate North America, Europe, or Asia, but does occur in the subtropics. The 15.5 Ma Vantage woods grew during one of the warmer intervals of the Miocene and this mixture of wood types indicates that while there was a seasonal climate, it was less pronounced than in the Late Miocene-Pliocene when many Asian elements disappeared from North America as the climate cooled. MAT estimates for Vantage based on the assemblage’s wood anatomical features are 12.1 and 12.8 °C, values within the range of the present-day Mixed Mesophytic forest type of eastern Asia. The Vantage assemblage shares genera with compression/impression and pollen floras of the Columbia Plateau, providing opportunities to eventually do whole plant reconstructions.
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Seventeen small, staminate flowers, 3.0–4.5 mm long × 1.0–1.5 mm wide, representing two developmental stages of the same type of flower have been recovered from the Middle Eocene Princeton chert locality of British Columbia. Some specimens are immature buds with overlapping perianth parts enclosing the stamens; others represent mature flowers with an open perianth. Flowers are pedicellate with a small flat receptacle bearing a perianth of at least three sepals and up to four petals. Five specimens show a three- to four-lobed rudimentary pistil surrounded by an intrastaminal nectary disk. The 10 stamens are included or barely exserted with nonconnate filaments, 1.2–2.0 mm long, attached by a slender connective to large dithecal anthers up to about 0.9 mm long that open by longitudinal slits. The anther wall is represented by a palisadelike endothecium composed of cells that are thick-walled and radially elongated relative to the long axis of the anther. Abundant in situ pollen is semitectate–columellate, tricolporate, subprolate to prolate, and prominently striated with equatorially bridged colpi. This fossil combines flower and pollen characteristics similar to those of the Sapindaceae, resembling most closely the tribe Dodonaeeae. Key words: Sapindales, Dodonaeeae, Tertiary, permineralization, flowers, pollen.
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A second species is added to Neviusia (Rosaceae: Kerrieae), previously known as a single rare species in the southeastern United States. The new species, N. cliftonii from northern California, differs from N. alabamensis primarily in having petals, fewer stamens, and more broadly ovate, coarsely toothed leaves. The relict nature of Neviusia is further supported by newly recognized fossils from the Eocene of British Columbia, Canada.