A new combination in Peristethium (Loranthaceae) expands the genus' range into the Amazon-Cerrado ecotone

Abstract

The genus Peristethium, characterized by determinate inflorescences protected by deciduous bracts, occurs in the northwest of South America, as well as Costa Rica and Panama. The main objective of this paper was to transfer one species to what we believe is its correct generic placement in Peristethium, that likewise implies in a shift of the genus' distribution beyond the Amazon. A new combination, Peristethium reticulatum, is proposed, based on Struthanthus reticulatus, described from Tocantins in 1980. The sexual dimorphism of the inflorescences of P. reticulatum (sessile male flowers and pedicellate female flowers) associated with male inflorescences that are inserted at leafless nodes are unique within the genus. The male flowers have dimorphic stamens, well-developed anthers and a pistiloid, whilst female flowers have robust styles and stigmas, and much reduced staminodes. Peristethium reticulatum and P. polystachyum occurs in the Amazon regions of Brazil, with the former recorded also in the ecotone with the Central Brazilian savannas (Cerrados).

Full text

169 VOL. 44(2) 2014: 169 - 174
A new combination in Peristethium (Loranthaceae)
expands the genus’ range into the
Amazon-Cerrado ecotone
Claudenir Simões
CAIRES
1
*, Kadja Milena GOMES-BEZERRA
2
, Carolyn Elinore Barnes PROENÇA
2
1
Universidade Estadual do Sudoeste da Bahia, Departamento de Ciências Naturais. Vitória da Conquista, Bahia, Brazil.
2
Universidade de Brasília, Instituto de Ciências Biológicas, Departamento de Botânica, Herbário UB. Brasília, DF, Brazil. biomilena@yahoo.com.br, cproenca@unb.br
* Corresponding Author: cscaires@hotmail.com
ABSTRACT
e genus Peristethium, characterized by determinate inorescences protected by deciduous bracts, occurs in the northwest
of South America, as well as Costa Rica and Panama. e main objective of this paper was to transfer one species to what
we believe is its correct generic placement in Peristethium, that likewise implies in a shift of the genus’ distribution beyond
the Amazon. A new combination, Peristethium reticulatum, is proposed, based on Struthanthus reticulatus, described from
Tocantins in 1980. e sexual dimorphism of the inorescences of P. reticulatum (sessile male owers and pedicellate female
owers) associated with male inorescences that are inserted at leaess nodes are unique within the genus. e male owers
have dimorphic stamens, well-developed anthers and a pistiloid, whilst female owers have robust styles and stigmas, and
much reduced staminodes. Peristethium reticulatum and P. polystachyum occurs in the Amazon regions of Brazil, with the
former recorded also in the ecotone with the Central Brazilian savannas (Cerrados).
KEYWORDS: Brazil, Floral dimorphism, Leaf architecture, Struthanthus.
Uma nova combinação em Peristethium (Loranthaceae) expande sua
distribuição até o ecótono Amazônia-Cerrado
RESUMO
O gênero Peristethium, caracterizado por inorescências determinadas protegidas por brácteas decíduas, ocorre no noroeste da
América do Sul, além da Costa Rica e Panamá. O objetivo do presente trabalho foi transferir uma espécie para o que acredita-se
ser seu correto posicionamento genérico em Peristethium, o que também implica em concomitante alteração da distribuição
geográca deste gênero para além da Amazônia. A nova combinação, Peristethium reticulatum, é proposta, baseada em
Struthanthus reticulatus, descrita para o Tocantins em 1980. O acentuado dimorsmo sexual das inorescências de P. reticulatum
(ores masculinas sésseis e as femininas pediceladas), juntamente com a origem de inorescências masculinas em nós álos
são únicos dentro do gênero. As ores masculinas apresentam estames dimorfos, anteras desenvolvidas e pistilódio, enquanto
as ores femininas possuem estiletes e estigmas robustos e estaminódio reduzido. Peristethium reticulatum e P. polystachyum
ocorrem em regiões amazônicas do Brasil, sendo a primeira registrada também em ecótono com o Cerrado.
PALAVRAS-CHAVE: Arquitetura foliar, Brasil, Dimorsmo oral, Struthanthus.

170 VOL. 44(2) 2014: 169 - 174  CAIRES et al.
A new combination in Peristethium (Loranthaceae) expands the genus’
range into the Amazon-Cerrado ecotone
e genus Peristethium was proposed by Tieghem (1895)
based on Loranthus leptostachyus Kunth, but the genus has
been largely ignored until its re-establishment by Kuijt (2012),
who proposed nine new combinations and described ve
new species. Amongst the 15 species currently recognized in
the genus, only P. polystachyum (Ruiz & Pav.) Kuijt occurs in
Brazil (Kuijt 2012; Caires and Dettke 2013).
During our studies of the Brazilian Loranthaceae, we
noted Struthanthus reticulatus, described by Rizzini (1980),
that conspicuous, deciduous, chartaceous bracts, which put
it within the modern circumscription of Peristethium (Kuijt
2012). Comparing its morphological characteristics with those
of the species treated by Kuijt (2012) we conclude that it
should be transfered to Peristethium. Peristethium reticulatum,
comprehensively treated in this paper, thus becomes the
second species of this genus to be recorded in Brazil.
e botanical collections of ten herbaria (BHCB, CEN,
IAN, INPA, MG, NY, RB, S, SPF, UB; see iers 2012 for
herbarium codes) were consulted. ose at NY were examined
on-line.
Specimens were analyzed under a stereoscopic microscope,
and the morphological terminology of Radford et al. (1974),
Rua (1999) and Kuijt (1981, 2012) adopted. A distribution
map was produced using ArcGIS 9.0; for specimens lacking
geographic coordinates these were inferred.
Leaves were cleared according to Shobe and Lersten
(1967), with modications according to Caires et al. (2012).
After clearing and staining, leaves were mounted between
sheets of glass following Paiva et al. (2006) and Gomes-
Bezerra et al. (2011). Leaf architecture terminology followed
Hickey (1974) and Ellis et al. (2009). To describe types of
sclerenchyma cells, the terminology of Kuijt and Lye (2005)
was followed.
Pollen grains analysis was done using a Scanning Electron
Microscope (JSM-7001F, JEOL Ltda, Akishima, Tokyo,
Japan) set to 15 KV with a working distance of 7-10 mm.
e pollen, obtained from inside the anthers, was xed on
stubs with carbon adhesive tape and metalized with gold in a
metalizer (Bal-Tec SCD-050, Balzers, Schaan, Liechtenstein).
Samples were described following the terminology of Barth
(1965), Feuer and Kuijt (1985) and Koch et al. (2009).
Peristethium reticulatum (Rizzini) Caires, comb. nov.
Struthanthus reticulatus Rizzini, Arq. Jard. Bot. Rio de Janeiro
24: 23. 1980. Type: Brazil, Northern Goiás [Tocantins], road
to Miracema do Norte [Miracema do Tocantins], cerrado,
parasite on G.T. Prance 58446 [Protium heptaphyllum (Aubl.)
Marchand], 28/VII/1964, owers green, G.T. Prance & N.T.
Silva 58445 (holotype RB; isotypes NY, UB!)
Shrub-like, robust hemiparasite, dioecious. Epicortical
roots not seen. Young stems compressed (transverse section
elliptic) to terete, glabrous; adult stems terete, glabrous,
smooth, grayish, with elliptical lenticels; nodes swollen,
with deep inorescence scars; internodes 2-4.5 x 0.2-0.4 cm.
Leaves opposite, decussate, rarely subalternate, coriaceous,
shiny in sicco, obovate to elliptic, apex shortly acuminate,
acuminate, acute or obtuse, sometimes somewhat retuse with
an apiculum (Pereira-Silva & Moreira 11312), base attenuate,
margin smooth, entire, 5.5-11 x 2.5-6 cm; festoonate
brochidodromous venation, the midvein sulcate on the
upper surface and prominent on the lower surface, venation
reticulate to the fourth order; secondary veins prominent and
conspicuous; petiole 5-10 x 1.5-2 mm. Male inorescences
axillary, rarely arising laterally at leaess nodes, protected by
deciduous bracts, 3 x 0.2 cm, these subtending 4-12 triads
and a terminal ower; sometimes, a pair of diads and a pair
Figure 1- Peristethium reticulatum (Rizzini) Caires. A. Habit. B. Bracts
subtending male inflorescences at leafless node. C. Bracts subtending axillary
male inflorescences. D. Young male inflorescence with conspicuous bracts.
E. Mature male inflorescence with bract scars. F. Male flower with pistiloid. G.
Female inflorescence. H. Female flower. I. Variation in the shape of the stigma.
J. Petal with staminode. K. Young fruit. L. Mature fruit. M. Endosperm. N.
Embryo (A: Krukoff 1494; B-C, F: Grogan 252; D: Lobato 1975; E, L-N: Fróes
26626; G-J: Fróes 26620; K: Thomas 4340).
5 mm
5 mm
5 mm
5 mm
5 mm
5 mm
2 mm
2 mm
2 mm
2 mm
2 mm

171 VOL. 44(2) 2014: 169 - 174  CAIRES et al.
A new combination in Peristethium (Loranthaceae) expands the genus’
range into the Amazon-Cerrado ecotone
of monads arising close to the apex, or just a pair of monads
and a solitary terminal ower; bracts chestnut, with whitish
margins, 2-3 x 1-2 mm. Male owers with green oral buds,
sessile, hexamerous, 6 x 1 mm, the base narrow and widening
towards the apex; stamens dimorphic, laments adnate to
the petals, with mbriate tufts at the base of the anther
(Figure 1F); anther tetralocular, connective not prolonged;
pistiloid present; pollen grains triangular, ca. 30 mm diam.,
surface psilate and verrucose. Female inorescences axillary,
protected by dehiscent bracts, 3-11 x 0.1-0.2 cm, supporting
3-8 triads, 1-2 diads and 1-2 monads and a single terminal
ower; sometimes lacking the triads; bracts chestnut to black
with a whitish margin. Female owers pedicellate, white or
yellow, hexamerous, 5 x 1 mm, cylindric, thin, staminodes
present or absent, stigma capitate; pedicel 2-10 x 0.5-1.5 mm.
Fruits 7-9 x 3-4 mm, smooth, ovoid to ellipsoid, immature
green, mature yellowish-orange, pale orange, red or black;
endosperm greenish, ellipsoid, 5 x 2 mm; embryo thin, 5 x
1 mm.
Additional specimens examined: Brazil. Amapá:
Oiapoque, estrada que vai para o aeroporto, 13/X/1950, .
female, R.L. Fróes 26620 (IAN, MG, UB); Ib., 13/X/1950,
. male, R.L. Fróes 26626 (IAN, MG, UB). Maranhão:
Estreito, Canteiro de obras próximo à pedreira, 6º35’25”S,
47º27’21”W, 150 m, fr., 08/III/2007, G. Pereira-Silva &
G.A. Moreira 11312 (CEN). Mato Grosso: Santa Terezinha,
Figure 2- Peristethium reticulatum (Rizzini) Caires: Optical microscopy
(A-B) and SEM (Scanning Electronic Microscopy) (C). A. Festoonate
brochidodromous venation. B. Leaf margins with details of the areoles (ar),
veinlets (ven), ultimate marginal vein (brace). C. Polar view of the pollen grain
(A-B: Fróes 26626; C: Grogan 252).
Figure 3.- Geographic distribution of Peristethium reticulatum (Rizzini) Caires
in Amazonia and the Cerrado-Amazon ecotone (black circles). Brazilian states:
AM = Amazonas, AP = Amapá, GO = Goiás, MA = Maranhão, MT = Mato
Grosso, PA = Pará, RO = Rondônia and TO = Tocantins.
hills of Serra do Tapirapé, 21 km SW of Portal do Amazonia
(jct MT413 to Santa Terezinha & BR158) along BR-158,
10º25’S, 51º27’W, 13/X/1985, fr., W.W. Thomas et al.
4340 (INPA, MG, SPF). Pará: Canaã dos Carajás, Floresta
Nacional de Carajás – Serra Sul, 6º19’14”S, 50º26’45”W,
725 m, 09/XII/2007, fr., N.F.O. Mota et al. 1137 (BHCB,
MG, UB); [Novo Progresso]: BR 163, Cuiabá-Santarém
Highway, km 884, northern foothills of Serra do Cachimbo,
11/XI/1977, fr., G.T. Prance et al. P25215 (MG); Pau D’arco,
Marajoara, . male, J. Grogan 252 (IAN, INPA, MG); São
Geraldo do Araguaia, Serra das Andorinhas, 03/XII/2001,
fr., D.D. Amaral et al. 177 (MG). Rondônia: Machadinho
[Machadinho D’Oeste], Distrito de Tabajara, estrada para
02 de novembro, 08/XI/1997, . male, L.C.B. Lobato et al.
1975 (MG); Ib., near Tabajara, upper Machado River region,
XI-XII/1931, fr., B.A. Kruko 1494 (S). Tocantins: Barra
do Ouro, margem esquerda do córrego do Ouro, 7º42’17’S,
47º38’27”W, 140 m, 02/IX/2008, . female, G. Pereira-
Silva et al. 13701 (CEN); Ib., 7º42’18”S, 47º38’28”W, 140
m, 19/VIII/2010, . female, J.B. Pereira et al. 213 (CEN);
Ib., Fazenda Santa Rosa, córrego Bacabal, 7º43’56”S,
47º42’16”W, 200 m, 04/IX/2008, fr., G. Pereira-Silva et
al. 13722 (CEN); Ib., 7º44’04”S, 47º42’17”W, 200m, 19/
XI/2010, fr., J.B. Pereira & J.P. Amaral 305 (CEN).
Peristethium reticulatum was found growing in terra rme
forest, dry or seasonally inundated gallery forests, white sand
elds (campinas de areia branca), shrubby canga vegetation
and in Central Brazilian savannas (Cerrado) (Pereira-Silva et
al. 13722). Recorded hosts are: Tapirira sp. (Anacardiaceae),
Humiriaceae, and Norantea sp. (Marcgraviaceae) as well as
Protium heptaphyllum (Aubl.) Marchand (Burseraceae) (Prance

172 VOL. 44(2) 2014: 169 - 174  CAIRES et al.
A new combination in Peristethium (Loranthaceae) expands the genus’
range into the Amazon-Cerrado ecotone
& Silva 58446). Hyperparasitism was recorded for Mota 1137
(UB), which was parasitised by Cuscuta sp. (Convolvulaceae).
Peristethium reticulatum is easily recognized in the eld as
a robust plant, with conspicuously lenticelate branches (Figure
1B) and deep scars from the previous years’ inorescences.
In herbarium specimens, the leaves are very shiny, with an
evident reticulum formed by the secondary and tertiary veins,
a feature used by Rizzini (1980) to choose the species epithet.
Analysis of cleared leaves showed festoonate brochidromous
venation, with veins to the fourth order (Figure 2A).
Secondary veins form 8-12 conspicuous, prominent pairs,
with a divergence angle of 45º-70º; the intersecondary veins
are exmedial and the tertiary veins are alternate-percurrent.
e areoles are well developed, with 4-6 sides (Figure 2B),
occurring at a density of c. 12/mm
2
; veinlets are dendritic
(Figure 2B). e ultimate marginal veins incomplete (Figure
2B). No bers, crystaliferous cells or sclereids were observed
in the leaf mesophyll, only terminal tracheids were found,
diering from those observed by Kuijt (2012) and Kuijt and
Lye (2005) in other species of Peristethium.
Male inorescences arise in the nodes of both new and
old branches, usually in the leaf axils (Figure 1C), but spikes
also arise from leaess nodes (see Fróes 26626, Grogan 252
and Lobato 1975; Figure 1B). All oral “units” (triads, diads
or monads) are protected by deciduous bracts, present in
young inorescences (Figure 1D) but fully deciduous in
mature inorescences (Figure 1E). In general, inorescences
are formed by several pairs of sessile triads (the owers are
also sessile), up to the last nodes before the terminal ower,
although 1-2 pairs of diads and sometimes 1-2 pairs of monads
are present.
Pollen grains are triangular in polar view, oblate-spheroidal
in equatorial view, c. 30 mm in diameter, surface psilate to
verrucose (Figure 2C), similar to those of Peristethium lojae
(Kuijt) Kuijt (Kuijt 2012).
Female plants have only one inorescence per leaf axil,
which is usually larger than the inorescences of male plants.
Female owers are all pedicellate and easily distinguishable
from the male owers by bud shape, the robust functional
pistil and extreme reduction of the stamens (staminodes)
(Figures 1H-J). Variability in inorescence units is common,
with some inorescences composed of several pairs of triads,
1-2 pairs of monads and a terminal ower (Figure 1A) or a
few pairs of diads, a single pair of monads and the terminal
ower (Figure 1G).
Peristethium reticulatum is distinct from the other species
of the genus by the complex inorescences formed from
dierent combinations of triads, diads and sessile monads,
the sessile male owers and the pedicellate female owers. It
is very similar to P. leptostachyum (Kunth) Tiegh., particularly
in oral morphology, but leaf morphology and obviously
pedicellate female owers distinguish the two taxa.
Key to the Brazilian species of Peristethium
1. Female owers pedicellate; male owers with pistiloid;
adult stems lenticellate .................................. P. reticulatum
1’. Female owers sessile; male owers without pistiloid;
adult stems smooth ................................... P. polystachyum
Peristethium reticulatum is reported from six Brazilian
states, all within the Amazon region. Only specimens collected
along the borders between the states of Tocantins (TO) and
Maranhão (MA) can be considered to be in the transitional
zone between the Amazon and the Cerrado biomes (Figure
3). Peristethium nitidum (Kuijt) Kuijt and P. roraimense
(Steyerm.) Kuijt occur on the border between Venezuela,
Guyana and near the northern borders of the state of Roraima
(Brazil), while P. reticulatum occurs on the frontier between
Amapá (Brazil) and French Guiana. ese three species, and
P. polystachyum, belong to a group of species that grow in the
Amazon lowlands, as opposed to the remaining species of
the genus that grow in the Andean regions of South America
(Kuijt 2012).
ACKNOWLEDGEMENTS
We thank the Laboratório de Microscopia Eletrônica da
Universidade de Brasília helpful sta, and herbarium curators
for loans, images furnished (specially Dr. Marcelo F. Simon)
and logistic support during our visits. CSC and KMG-B thank
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
(CAPES) for Ph. D. scholarships. is is publication 8 in the
Parasitic Plants Research Group technical series.
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Recebido em 25/01/2013
Aceito em 19/06/2013