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The Caribbean Gesneriaceae: an update on the classification of Gesneria and Rhytidophyllum. Gesneriads

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Third Quarter 2020 1
Gesneriads
Volume 70 ~ Number 3
ird Quarter 2020
The Journal for Gesneriad Growers
Return to Table of Contents
Gesneriads
The Journal for Gesneriad Growers Volume 70 ~ Number 3
ird Quarter 2020
Return to Table of Contents
Front Cover
Front view of ower of Gesneria fruticosa
(from Haiti) featuring mbriate corolla
lobes. Photographed by John L. Clark.
See article, page 10.
Back Cover
Back view of ower of Gesneria ekmanii (from
Haiti) featuring resin deposits.
Photographed by John L. Clark.
See article, page 10.
Editor
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Contributing Editors
Arleen Dewell,
Jeanne Katzenstein,
Charlene Marietti,
Dale Martens, Norah Otto,
Paul Susi, Mary Jo Modica
Consulting Taxonomist
Dr. Laurence E. Skog
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FEATURES
5 Annual Membership Meeting
6 Registering Gesneriads –
Not Just for the Hybridizers!
Ron Myhr
10 The Caribbean Gesneriaceae: an
update on the classification of
Gesneria and Rhytidophyllum
John L. Clark
27 Houston African Violet and Gesneriad
Society – Our Newest Chapter
Sam Cunningham
30 “Thinking Outside the Box – When
Growing Gesneriads”
Karyn Cichocki
39 Growing Streptocarpus
porphyrostachys
Hung Nguyen
42 Gesneriads at the Philadelphia
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46 Glandular Trichomes in Kohleria
Minh Bui
DEPARTMENTS
3 A Message from the President
4 From the Editor
21 Chapters and Affiliates
Karyn Cichocki
22 Gesneriad Registrations
Irina Nicholson
26 Coming Events
Ray Coyle and Karyn Cichocki
52 Back to Basics: Leaf Trimming
Dale Martens
54 Seed Fund Contest Winners for 2019
55 Seed Fund – Species
Carolyn Ripps
60 Changes to Hybrid Seed List 2Q 2020
61 Information about The Gesneriad
Society, Inc.
10 Gesneriads ~ Volume 70 ~ Number 3Return to Table of Contents
The Caribbean Gesneriaceae: an
update on the classification of
Gesneria and Rhytidophyllum
John L. Clark ~ Aldo Leopold Distinguished Teaching Chair, Science
Department, The Lawrenceville School, Lawrenceville, NJ, USA ~
<jclark@lawrenceville.org>
GESNERIADS ARE BOTANICAL JEWELS
of the Caribbean ora. eir broad range of ower
shapes and colors do not conform to traditional
generic concepts. Habits range from terrestrial
shrubs that are more than two meters tall (Fig. 1A)
to miniature rosettes that are smaller than a human
palm (Fig. 1B) to obligate lithophytes (restricted
to rocks or clis). Eccentric ower colors are
represented by Gesneria heterochroa, which has
green corolla tubes with white lobes (Figs. 1C &
D), and Gesneria clarensis, which has orange corolla
tubes with green lobes (Figs. 1E & F).
Gesneria and Rhytidophyllum share a recent
common ancestor (along with Pheidonocarpa
and Bellonia) and are classied in the subtribe Gesneriinae (Weber et al., 2013, 2020).
Current estimates suggest that Gesneria has 65 species, and Rhytidophyllum has 25
species (Clark et al., 2020). e current taxonomy of Gesneria is based on a monograph
published more than four decades ago (Skog 1976), which is more recent compared to
Rhytidophyllum that was last monographed in the late 19th century (Hanstein 1865).
e entire Caribbean Gesneriaceae could be considered a taxonomist’s nightmare
because of ongoing changes in classication. Likewise, this group is a cherished dream
for evolutionary biologists because of convergent evolution, remarkable patterns of
species diversication, and a broad range of plant-pollinator interactions. A goal of this
article is to share information about Gesneria and Rhytidophyllum, the dominant genera
of Caribbean Gesneriaceae. I will describe recent classication changes, and highlight
those changes with images, many of which are documented here from live material
during recent exploratory research expeditions. A more comprehensive background on
the classication of these two genera is found in Wiehler (1983) and Skog (1976). Skog’s
Ph.D. dissertation focused on a comprehensive taxonomic treatment of Gesneria (Skog
1976) that included eld expeditions in 1970 to Puerto Rico, Dominica, Dominican
Republic, Haiti, and Jamaica. Important discoveries from those expeditions were
described in e Gloxinian, now Gesneriads, by Skog and Talpey (1973).
Gesneria and Rhytidophyllum are sister groups (i.e., share a recent common ancestor),
and, as a result of their close relationship, they share many distinguishing features. e
following list of characters (Fig. 2) dierentiates them from all other members of the
New World Gesneriaceae.
1) e ovaries are inferior in Gesneria and Rhytidophyllum. Inferior means that the
ovary is below the attachment of the petals and sepals (Fig. 2A). In contrast, most New
World Gesneriaceae, with very few exceptions, have superior ovaries. Superior means
that the ovary is above the attachment of the petals and sepals (Fig. 2B).
Third Quarter 2020 11Return to Table of Contents
Figure 1. Variation of habit and corolla colors found in Gesneria and Rhytidophyllum.
A. Tree habit of Rhytidophyllum grandiflorum. B. Rosette habit of Gesneria reticulata.
C and D. Gesneria heterochroa. E and F. Gesneria clarensis.
12 Gesneriads ~ Volume 70 ~ Number 3Return to Table of Contents
Figure 2. Characters that distinguish Rhytidophyllum and Gesneria from most New World
Gesneriaceae. A, C, and E. are Gesneria/Rhytidophyllum and B, D, and F. are other New World
Gesneriaceae. A. Inferior ovary where ovary is below the attachment of the petals and sepals
(Gesneria bicolor). B. Superior ovary where the ovary is above the attachment of the petals and
sepals (Crantzia cristata). C. Leaf arrangement alternate (Rhytidophyllum acunae).
D. Leaf arrangement opposite (Neomortonia rosea). E. Subwoody capsule (Gesneria depressa).
F. Fleshy display capsule (Drymonia brochidodroma), one of a variety of fleshy fruit types in
New World Gesneriaceae.
Third Quarter 2020 13Return to Table of Contents
Figure 3. Selection of flowers featuring corolla lobe fimbriations and resin deposits of
arborescent (=shrubby) species of Gesneria. A and B. Gesneria duchartreoides (from Cuba).
C and D. Gesneria odonotophylla (from Haiti). E and F. Gesneria ekmanii (from Haiti).
F and G. Gesneria viridiflora (from Cuba).
14 Gesneriads ~ Volume 70 ~ Number 3Return to Table of Contents
2) e leaf arrangement in Gesneria and Rhytidophyllum is alternate (Fig. 2C). In
contrast, most other New World Gesneriaceae are characterized by opposite leaves (Fig.
2D).
3) e fruits in Gesneria and Rhytidophyllum have woody capsules (Fig. 2E). In
contrast, most fruits of New World Gesneriaceae have eshy berries or eshy capsules
(Fig. 2F), with few exceptions.
4) e nectary for Gesneria and Rhytidophyllum is annular (Fig. 4H). In contrast,
nectaries for most other New World genera are lobed. Examples include ve separate
lobes (esp. Columnea) to bilobed or single-lobed on the upper surface of the ovary.
Gesneria and Rhytidophyllum diversied in the Caribbean, and their presence in South
or Central America is rare. ey are almost entirely endemic to the Caribbean except for
the following two species: 1) Rhytidophyllum onacaense is endemic to northern Colombia,
where it is known from fewer than ten collections (only three from the last century) at
the base of the Sierra Nevada de Santa Marta, a mountain range that is isolated from the
Andes; 2) Rhytidophyllum cumanense is mostly known from Venezuela.
Recognizing Gesneria and Rhytidophyllum is relatively easy because of many
shared derived characters (Fig. 2). In contrast, the distinction between Gesneria and
Rhytidophyllum involves more careful evaluation. Taxonomists have diered on whether
they should be combined as one large genus or retained as separate genera. Wiehler
(1983) preferred a system of one genus (i.e., lumping “Rhytidophyllum” as a subgroup of
Gesneria). e primary reason for Wiehler’s support of a single genus classication was
based on the absence of a unifying character that dened or dierentiated Gesneria and
Rhytidophyllum.
In contrast, Skog (1976) had published a comprehensive treatment of Gesneria
where he recognized Gesneria and Rhytidophyllum as distinct genera. Also, Skog (1976)
described the new genus, Pheidonocarpa, to accommodate a single species that did not t
the currently accepted genera. Although not the focus of this article, the recognition of
Pheidonocarpa is supported as a monophyletic lineage based on molecular phylogenetic
studies (Joly et al., 2017; Marten-Rodriguez et al., 2010; Watson 2015).
Gesneria flowers in the wild are different from what is known in
horticulture
ere are many ower types in Gesneria, but most of the species readily available in
horticulture are characterized by red tubular owers and rosette habits (e.g., G. reticulata
and G. cuneifolia). e shrub habit ofGesneriais rare in cultivation, and the owers of
these species are not typical of material that is more readily available in cultivation. Many
shrubs of Gesneria have campanulate (bell-shaped) owers that are coriaceous (leathery).
e outer surfaces of the owers of the shrubby species appear waxy because they are
covered with resin deposits (Fig. 3 and back cover). A selection of campanulate corollas
with resin deposits is featured in Figure 3. Another character of many Gesneria owers is
the presence of mbriations along the margins of the corolla lobes (Figs. 3B, F, and H).
Rhytidophyllum flowers
e owers of Rhytidophyllum are mostly campanulate (bell-shaped), with tubes that are
greenish-yellow or yellow suused with purple splotches (Fig. 4). Another useful feature
for recognizing Rhytidophyllum is that abundant populations often grow in full sunlight
along secondary roads (Fig. 1A). It is relatively easy to observe Rhytidophyllum on a fast-
moving bus where clumps of populations of 30-50 individuals are common. e stems
are stout and erect, and the leaves are covered with viscous (sticky) hairs. Unlike the
ephemeral owers of many Gesneria, the owers of Rhytidophyllum are usually persistent
and easily observed above tufts of terminally clustered leaves.
Rhytidophyllum that are terrestrial shrubs can be more than two meters tall (Fig.1A).
Third Quarter 2020 15Return to Table of Contents
Figure 4. Rhytidophyllum flowers. A and B. Rhytidophyllum crenulatum. C and D.
Rhytidophyllum rhodocalyx. E and F. Rhytidophyllum auriculatum. G. Walls of Morro
Castle, entrance of Havana Bay, Cuba where Rhytidophyllum crenulatum grows in abundant
populations. H. Annular nectary of Rhytidophyllum exsertum.
16 Gesneriads ~ Volume 70 ~ Number 3Return to Table of Contents
Figure 5. Filament character for Rhytidophyllum and Gesneria. A. Rhytidophyllum crenulatum
featuring filaments adnate to the corolla tube with barbate hairs (indicated with arrows).
B and C. Gesneria depressa (B) and Gesneria salicifolia (C) featuring filaments separate from
the corolla tube and glabrous filaments (indicated with arrows).
Third Quarter 2020 17Return to Table of Contents
Lithophytes (rock dwellers) represent a habit that is dierent from the more common
terrestrial shrubs. Rock dwellers are smaller (usually less than 60 cm tall) than their
terrestrial relatives. One of my favorite rock-dwellers and most readily observed species
is Rhytidophyllum crenulatum that covers the walls of the Morro Castle near the entrance
to Havana Bay in Havana, Cuba (Fig. 4G). A selection of Rhytidophyllum owers is
featured in Figure 4.
Characteristics differentiating Gesneria and Rhytidophyllum
Molecular phylogenetic studies (Martén-Rodríguez et al., 2010; Watson 2015;
Joly et al., 2017) have mostly supported a sister-group relationship of Gesneria and
Rhytidophyllum, but taxon sampling is limited and statistical support is low. A more
comprehensive taxon sampling to evaluate Gesneria and Rhytidophyllum is an ongoing
collaborative project by several botanists (e.g., Joly, Clark, and Martèn-Rodriguez.)
Several morphological characters reect a separation. e most useful character to
dierentiate Gesneria and Rhytidophyllum is the presence or absence of fusion of
laments to the corolla tube (Fig. 5). e term connation is used to describe similar parts
that are fused (e.g., the fusion of petals to form a corolla tube as in most members of the
Gesneriaceae). e term adnation is used to describe the fusion of dissimilar parts, such
as the fusion of laments to the corolla tube. e character that denes Rhytidophyllum is
the presence of laments that are adnate for 2-5 mm to the base of the corolla tube (Fig.
5A). e character that denes Gesneria is free laments or complete lack of fusion (i.e.,
absence of adnate laments to the corolla tube) (Figs. 5B & C). Fig. 5A features an open
ower of Rhytidophyllum crenulatum where you can observe a zone of adnation for 2-3
mm near the base of the corolla and a zone where the laments are free from the corolla
tube. ese two regions (i.e., separate laments that are above the zone of adnation) are
indicated on both sides of an opened corolla tube (Fig. 5A). In contrast, the laments in
Gesneria are free or separate from the entire length of the laments (Figs. 5B and C) and
therefore have no zone of adnation.
Another character that is useful for dierentiating Rhytidophyllum is clusters of
barbate (bearded) hairs at the base of the laments and immediately above the zone of
adnation. In Gesneria, the base of the laments is glabrous (without hairs). Barbate clusters
of hairs are indicated with white arrows (Fig. 5A) or lack thereof (Figs. 5B and C).
Images of Rhytidophyllum featuring adnate laments to the corolla tube and barbate
trichomes are featured in Figure 5A. Images of Gesneria featuring free laments that are
glabrous are featured in Figures 5B and C.
Convergent evolution and the presence of red flowers in
Gesneria and Rhytidophyllum
One dierence between the generic concept presented here and those of Skog (2012)
is a complex of three red-owered species that are more recently (Clark et al., 2019;
2020) recognized as belonging to Rhytidophyllum. It is important to note that Morton
(1957a; 1957b) and early publications by Skog (1976) are congruent with the generic
concepts presented here. Ideas on generic concepts have changed, and phylogenetic
or evolutionary trees are an essential method for accepting or rejecting classications
based on relationships. In the example presented here, the presence of red owers is not
a shared derived character, and it does not suggest a close relationship – especially in
gesneriads that share the same geographic range.
ese three species (Rhytidophyllum earlei, R. lomense, and R. rupincola) are often
misplaced by horticulturists as members of Gesneria because of their red tubular corollas.
In contrast, these three species have red tubular owers but also have features that are
typical in Rhytidophyllum. e laments of Rhytidophyllum earlei, R. lomense, and R.
rupincola are adnate to the corolla tube with clusters of barbate hairs at base of laments.
18 Gesneriads ~ Volume 70 ~ Number 3Return to Table of Contents
Figure 6. Tubular red flowers in Gesneria (C and E) and Rhytidophyllum (A, B, D and F).
A. Rhytidophyllum lomense. B. Rhytidophyllum earlei. C. Gesneria libanensis.
D and F. Rhytidophyllum rupincola. E. Gesneria libanensis.
Third Quarter 2020 19Return to Table of Contents
us, the owers are red (not typical in Rhytidophyllum), but the laments are barbate
above the zone of adnation to the corolla tube (typical in Rhytidophyllum). Photographs
and descriptions provided here explain this remarkable example of convergent evolution,
and how this has resulted in the back-and-forth of their generic placement as members
of Rhytidophyllum and Gesneria. ese three species were the basis for the discrepancy
between recognizing one large genus (sensu Wiehler, 1983) versus two distinct genera
(sensu Skog, 1976). A recent dissertation explored these discrepancies in more detail
(Watson 2015), and provided here is a simplied summary.
It is important to note that phylogenetic analyses provide an objective framework for
evaluating generic concepts. Previous traditional concepts are likely to depend on a single
character with multiple origins (e.g., convergent evolution). It is challenging to dene
any group by a single morphological feature without evaluating its evolutionary history.
For example, not all columneas have berries (e.g., Columnea dielsii has a eshy capsule).
Not all drymonias have poricidal anther dehiscence (e.g., there are multiple reversals to
longitudinal slits as outlined in Clark et al., 2015). A single character will not readily
dene the diversication and evolution of Gesneria and Rhytidophyllum. When these
genera are evaluated in a phylogenetic context, red tubular owers are likely convergent.
eir presence in Gesneria and Rhytidophyllum is explained by multiple origins or
convergent evolution.
Single character systems that dene genera have been supplanted and supplemented
by phylogenetics. e use of evaluating characters in the context of evolution provides a
more objective and robust system for classication. For example, bats and birds y, but
the presence of ight is not because they share a recent common ancestor. Likewise, it
is crucial to understand morphological features in the Gesneriaceae in the context of
evolutionary relationships.
e red tubular owers of Rhytidophyllum lomense (Fig. 6A), R. earlei (Fig. 6B),
and R. rupincola (Fig. 6D and F) look like the red tubular owers of Gesneria libanensis
(Fig. 6C and E). e similar shapes and colors are independently derived, and that
is best explained in the context of an evolutionary tree (Martén-Rodríguez et al.,
2010; Watson 2015; Joly et al., 2017). e presence of red owers in this example is
convergent in Gesneria and Rhytidophyllum. at is why it is crucial to evaluate the
lament character when determining their proper generic placement. e red-owered
species of Rhytidophyllum (e.g., R. lomense, R. earlei, and R. rupincola) retain the
lament characteristics of other Rhytidophyllum such as adnation to the corolla tube and
barbate hairs above the zone of adnation (Fig. 6F). Even though these three species of
Rhytidophyllum have red tubular owers that appear like Gesneria libanensis (Fig. 6C),
they share a more recent common ancestor with members of Rhytidophyllum.
Recommendation
If Caribbean gesneriads pique your interest, then I encourage you to read Skog (1976),
where historical literature, nomenclature, taxonomy, species descriptions, and pollination
biology are covered for Gesneria and Rhytidophyllum. Likewise, recent literature has
transformed current concepts on the pollination and diversication of Caribbean
gesneriads (cf., Martén-Rodríguez & Fenster 2008, 2010; Martén-Rodríguez et al. 2010,
2015; Lambert et al. 2017; Alexandre et al. 2018; Joly et al. 2018). Hopefully, some of
the shrubby species that are typical in the Caribbean and rarely found in cultivation may
soon be available. Most importantly, I hope that the forests that harbor these remarkable
gesneriads are preserved and maintained in perpetuity for current and future generations.
Acknowledgements
Laurence E. Skog, Jeanne Katzenstein, Ron Myhr, Jacqi Haun, and Silvana Clark are
acknowledged for providing their editorial expertise and helping to make the manuscript
20 Gesneriads ~ Volume 70 ~ Number 3Return to Table of Contents
friendly to a broad audience of horticultural enthusiasts. Tom Talpey provided the
images from Figures 1A and B that were taken during his exploratory expeditions to
several Caribbean countries throughout the 1960s. Tom graciously shared his 1300+
Kodachrome slide collection featuring many gesneriads that he introduced into cultivation.
Literature cited
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unrelated to pollination syndromes in Antillean Gesneriaceae. Royal Society Open Science 4: 170293.
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Scientic Books.
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theGesneriaceae (Subfamilies Sanangoideae andGesnerioideae). Rheedea 30: 190-256.
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species from Puerto Rico. Annals of Botany 102: 23-30.
Martén-Rodríguez, S. and C. Fenster. 2010. Pollen limitation and reproductive assurance in Antillean
Gesnerieae: a specialist vs. generalist comparison. Ecology 91: 155-165.
Martén-Rodríguez, S., C. Fenster, I. Agnarsson, L.E. Skog, and E. Zimmer. 2010. Evolutionary
breakdown of pollination specialization in a Caribbean plant radiation.New Phytologist188: 403-
417.
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comparison of reproductive strategies between island and mainland Caribbean Gesneriaceae. Journal
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Morton, C.V. 1957b. Gesneriaceae. Pp. 451-472 in H. León and H. Alain, eds. Flora de Cuba, Volume
4. Imp. P. Fernandez y Cía, La Habana, Cuba.
Skog, L.E. and T. Talpey.1971. Rediscovery of Gesneria humilis. e Gloxinian. 21: 7-9.
Skog, L.E. 1976. A study of the tribe Gesnerieae, with a revision of Gesneria (Gesneriaceae:
Gesnerioideae). Smithsonian Contributions to Botany 29: 1-182.
Skog, L.E. 2012. Gesneriaceae. Pp. 350-364 in P. Acevedo-Rodriguez and M.T. Strong, eds. Catalogue
of Seed Plants of the West Indies. Smithsonian Contributions to Botany. 98: 1-1192.
Watson, R. 2015. Resolving generic boundaries in Rhytidophyllum and Gesneria: a molecular phylogeny
of the Caribbean subtribe Gesneriinae (Gesneriaceae). Unpublished master’s thesis. e University of
Alabama, Tuscaloosa, AL.
Weber, A., J.L. Clark, and M. Möller. 2013. A new formal classication of Gesneriaceae. Selbyana 31:
68-94.
Weber, A., D.J. Middleton, J.L. Clark, and M. Möller. 2020. Keys to the infrafamilial taxa and genera of
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The Shopping Mall
“OZARK” Sinningias, African Violets
and other Gesneriads. Dave’s Violets,
1372 S. Kentwood Avenue, Springeld,
MO 65804 (417) 887-8904 Email:
<plantman@ipa.net> (no catalog).
www.davesviolets.com.
MRS STREP STREPS – Streptocarpus,
Primulinas, and other Gesneriads. Email
for list of available plants. Kathy Spiss-
man, 4086 Brownlee Dr., Tucker, GA
30084. Phone (770) 939-5289. Email:
<mrsstrepstreps@comcast.net>.
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