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Carnevali Fernández-Concha et al. / Botanical Sciences
Botanical Sciences
DOI: 10.17129/botsci.3300
Received: February 15, 2023, Accepted: March 24, 2023
On line rst: May 20, 2023
Taxonomy and Floristics / Taxonomía y Florística
This is an open access article distributed under the terms of the Creative Commons Attribution License CCBY-NC (4.0) international.
https://creativecommons.org/licenses/by-nc/4.0/
Centrosema flavesCens (Fabaceae, PaPilionoideae), a new sPecies
From the Yucatan Peninsula, mexico
Centrosema flavesCens (Fabaceae, PaPilionoideae), una nueva esPecie
de la Península de Yucatán, méxico
Germán carnevali Fernández-concha1,2, dieGo F. anGulo1, José luis taPia muñoz1,
ivón m. ramírez morillo1, and rodriGo duno de steFano1*
1 Herbarium CICY, Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A.C., Mérida, Yucatán, Mexico.
2 Orchid Herbarium of Oakes Ames, Harvard University Herbaria, Cambridge, Massachusetts, USA.
*Corresponding author: roduno@cicy.mx
Abstract
Background: Centrosema (Fabaceae) includes 35-44 species in the New World, 10 in Mexico, and 9 in the Yucatan Peninsula. Most species
have trifoliolate leaves and bicolored flowers. Unifoliolate leaves are an infrequent character that is found in a few species, e.g., C. sagittatum
(Humb. & Bonpl. ex Willd.) Brandegee, but monochromatic flowers, e.g., lacking nectar guides, is even a more unusual character state.
Several populations of a Centrosema from the Yucatan Peninsula share both character states, a combination that sets them apart from other
members of the genus.
Question: Is the Centrosema with unifoliolate leaves, alate petioles, and monochromatic owers of the Yucatan Peninsula, a species distinct
from the phenetically similar C. sagittatum?
Studied species: Centrosema (Fabaceae, Papilionoideae).
Study site and dates: Yucatan Peninsula, Mexico, 2021-2023.
Methods: Botanical specimens were collected and determined taxonomically through the use of relevant literature, keys, and the consulting of
botanical collections. The conservation status of the new species was assessed using the IUCN methodology.
Results: The specimens collected do represent an undescribed species that differs from Centrosema sagittatum by its smaller, cream-yellow,
monochromatic owers. The species is assessed as Endangered (EN).
Conclusions: A new species, Centrosema avescens from the Yucatan Peninsula is proposed. Eleven species of Centrosema are now recognized
in Mexico, nine in the Yucatan Peninsula. C. sagittatum does not occur in the Yucatan Peninsula.
Kew Words: Leguminosae, Papilionoideae, taxonomic novelty, Yucatán.
Resumen:
Antecedentes: Centrosema (Fabaceae) es un género de 35-44 especies en el Nuevo Mundo, 10 en México y 9 en la península de Yucatán. La
mayoría de las especies tienen hojas trifolioladas y ores bicolores. Las hojas unifolioladas son un carácter poco frecuente que se encuentra en
pocas especies; p.ej. C. sagittatum (Humb. & Bonpl. ex Willd.) Brandegee, pero las ores monocromáticas, que carecen de guías de néctar, es
incluso un estado de carácter más inusual. Varias poblaciones de Centrosema de la península de Yucatán comparten ambos estados de carácter,
una combinación que las separa de otras especies del género.
Pregunta: ¿Es el Centrosema de hojas unifolioladas, pecíolos alados y ores monocromáticas de la península de Yucatán una especie diferente
de la fenéticamente similar C. sagittatum?
Especies de estudio: Centrosema (Fabaceae, Papilionoideae).
Sitio de estudio y fecha de estudio: Península de Yucatán, México, 2021-2023.
Métodos: Se recolectaron especímenes botánicos y se determinaron taxonómicamente mediante el uso de literatura relevante, claves y la con-
sulta de colecciones botánicas. El estado de conservación de la nueva especie se evaluó utilizando la metodología de la UICN.
Resultados: Los especímenes colectados representan una especie no descrita que se diferencia de C. sagittatum por las ores cremosas, mono-
cromáticas y más pequeñas. La especie es evaluada como En Peligro (EN).
Conclusiones: Se describe una nueva especie, Centrosema avescens, de la península de Yucatán. Se reconocen once especies de Centrosema
en México y nueve en la península de Yucatán. Centrosema sagittatum no crece en la península de Yucatán.
Palabras clave: Leguminosae, novedad taxonómica, Papilionoideae, Yucatán.
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Centrosema avescens a new species from Mexico
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Centrosema (DC.) Benth. (Fabaceae: Papilionoideae: Phaseoleae) is one of the ve genera of the subtribe
Clitoriinae Benth. (Schrire 2005), three of which are found in Mexico: Barbieria DC., Centrosema, and
Clitoria L. (Villaseñor 2016). All ve genera feature resupinate owers, which are uncommon in the Pa-
pilionoideae. Centrosema is characterized by having a at or more or less convex banner (never deeply
concave), with a dorsal short or gibbous spur, a bell-shaped calyx, wings shorter in length than the keel petals, and a
broad “U”-shaped style. The fruits are sessile, at and with two ribs near each margin (McVaugh 1987, Barreto et al.
2018). The name Centrosema comes from two Greek words: kentron, meaning spur and sema, meaning signal, prob-
ably referring to the small spur at the base of each petal. It can also refer to the central nectar guides of the banner.
Centrosema includes about 35-44 species distributed in the New World, some of which have naturalized in tropi-
cal Africa, Asia, and Oceania (Barreto et al. 2020, POWO 2023 www.plantsoftheworldonline.org). In Mexico, 10
species were them known (Villaseñor 2016), nine of which grow in the Yucatan Peninsula (Duno de Stefano et al.
2008, Carnevali et al. 2010).
In 2020 we visited the village of Chan Yokdzonot, near Valladolid, in the state of Yucatán, and collected a Cen-
trosema with monochromatic owers (Figures 1D, 2). Most of the Mexican species of this genus have leaves with
three leaets, with few exceptions, and the most striking is C. sagittatum (Humb. & Bonpl. ex Willd.) Brandegee
with one leaet and a winged petiole. As described in the available literature and iconography, this species has white
owers with purple or reddish nerves or longitudinal spots (nectar guides) on the central portion of the “labellum”
(the banner). Carnevali Fernández-Concha et al. (2021) considered this plant an albino form of this species, but
pending further evaluation. For these reasons, we reevaluate the taxonomy of C. sagittatum from the Yucatan region.
The main purposes of this article are four: 1) To compare the morphology of the Centrosema population of Chan
Yokdzonot and other localities in the Mexican Yucatan peninsula with the other species of the genus, but especially
with C. sagittatum. 2) If warranted, to propose a new species of Centrosema including a detailed description, dis-
cussion of similarities, and relevant iconography. 3) To provide good photographic material of the species of Cen-
trosema from the Mexican Yucatan Peninsula. 4) To provide a key for the identication of the Centrosema species
of the area.
Materials and methods
Field and herbarium work. The study was conducted at Herbarium CICY of the Centro de Investigación Cientíca
de Yucatán, A.C. (CICY), Yucatán, Mexico. Plants and other materials were obtained under scientic permits (SGPA/
DGVS/01280/21 and SGPA/DGGFS/712/2913/17) issued by the Secretaría de Medio Ambiente y Recursos Natura-
les (SEMARNAT) to researchers at CICY. Photographs were produced by GC with the use of a Nikon 3300 camera.
We examined approximately 50 herbarium specimens from the Yucatan Peninsula deposited in the Centrosema
collection at herbaria CICY, UADY, and UCAM (acronyms follow Thiers 2020). All type specimens, as well as
general collections, hosted by virtual herbaria, were consulted, including those maintained by JSTOR Global Plants
(plants.jstor.org), Reora Virtual Herbarium (reora.jbrj.gov.br), speciesLink (specieslink.net), and Universidad Na-
cional Autónoma de México (MEXU; datosabiertos.unam.mx/biodiversidad).
General taxonomic literature on Centrosema was consulted; in particular, Fantz (1996, 2001, 2004), Duno de Ste-
fano et al. (2008). Also, Neotropical bibliographic sources were analyzed: Barbosa-Fevereiro (1977), Fantz (1999,
2001), Barreto et al. (2020). Additionally, the International Plant Names Index (www.ipni.org), and Tropicos (tropi-
cos.org) were consulted to update the current nomenclature and geographical information, as well as evaluate and use
photographic and morphological (particularly color description) information therein. Finally, the general color of the
ower and of the nectar guides was assessed with the color chart of Exotica (Graf 1966).
A geographic distribution map was created using the software QGIS v.3.26.2 (QGIS Development Team 2023
www.qgis.org) with base map tiles by Stamen Design (maps.stamen.com). Whenever necessary, geographic coordi-
nates were estimated from label data on herbarium specimens using Google Earth Pro 7.3.2.5776. The occurrence
data used in the map were obtained from GBIF (www.gbif.org).
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Figure 1. Morphology of some Centrosema species from the Yucatan Peninsula (including C. sagittatum for comparison). A-B. C. angustifolium, A. leaves
B. ower, front view. C. C macrocarpum, owers, front view, D. C. avescens, leaves. E-F. C. plumieri, E. ower front view. F. ower back view. G-H.
C. schottii, G. leaves and owers, H. ower front view and back view showing two bracteoles. I-J. C. sagittatum, I. leaves. J. ower, front view. K-L. C.
virginianum, leaves and ower. Photos: A-B, H. Gustavo A. Romero-González. C-D, G, Germán Carnevali. E-F, K-L. Alfredo Dorantes Euán. I-J. Edgar
Ramón Gómez Vega.
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Morphological analysis. Descriptions were compiled mainly from living specimens supported by herbarium vouch-
ers. The type specimen of the new species was cultivated successfully at a private collection. Some additional owers
from herbarium material were rehydrated by boiling and then soaking them in a soapy solution. All material was
examined under a dissecting microscope. Pretreated owers were temporarily pickled for further study and eventu-
ally returned to herbarium sheets.
Conservation assessment. The conservation status of the new species was assessed using the IUCN Red List Criteria
(IUCN 2012, 2020). We relied on criterion B, geographical distribution assessed both as B1 (extent of occurrence)
or B2 (area of occupancy), as implemented in GeoCAT (Bachman et al. 2011). We complemented these assessments
with our own eld experience, published data, and iconography, whenever available.
Results
Centrosema includes 35-44 species (Barreto et al. 2020, POWO 2023 www.plantsoftheworldonline.org). The ge-
nus includes about 35 species with trifoliolate leaves (e.g., Centrosema acutifolium Benth., C. pascuorum Mart. ex
Benth., C. pubescens Benth., and C. virginianum (L.) Benth.), two species with 3-palmate leaves (C. bracteosum
Benth., and C. venosum Mart. ex Benth.), one species with 5-7-foliolate leaves (C. heptaphyllum Moric.), and lastly,
ve species with unifoliolate leaves (C. carajasense Cavalc., C. fasciculatum Benth., C. sagittatum, C. tapirapoa-
nense Hoehne, and C. unifoliatum (Rose) Lundell). In all cases, the unifoliolate condition is achieved by reduction of
the lateral folioles of a normally trifoliolate leaf. Centrosema unifoliatum is the most distinct among the unifoliolate
species: a plant with a terete petiole and very narrowly oblong to linear leaets. Both C. carajasense and C. fas-
ciculatum have winged petioles, and, despite the base of the leaet being cordate, the leaet overall outline is never
sagittate. Only C. sagittatum has both winged petioles and sagittate leaves and it is thus easy to associate the Yucatan
plants with C. sagittatum (Figures 1 I-J).
Here we are basing our species conceptualization on the Unied Species Concept (de Queiroz 2007). Thus, any
new taxon is a hypothesis of relationships between taxa at a lower rank. Species are seen as groups of individuals or
populations that are hypothesized to be more closely related to each other than to other individuals or populations that
we would refer to different species. The proposed relationship is supported by evidence provided from phylogenetic,
ecological, biogeographic, and morphological data and characters, which identify the proposed taxon as distinct
from closely related taxa and evidence its status as a lineage (or lineages) with an independent evolutionary history,
adapted to a particular niche in its own geographical and ecological context.
In the case of the taxon herein proposed, it shares the unifoliolate, sagittate leaf with the winged petiole with the
phenetically similar Centrosema sagittatum. However, it has pale cream-yellow owers that are monochromatic,
e.g., they lack the usual-colored nectar guides (lavender) that characterize C. sagittatum. There is also geographical
coherence in the distribution of this color morphotype and is apparently restricted to the Yucatan Peninsula Biotic
Province as dened by Carnevali et al. (2010) and it is disjunct from C. sagittatum. Furthermore, there are additional
morphological differences, described below, that support the recognition of this entity as a new taxon.
Centrosema avescens Carnevali, Duno & Angulo, sp. nov (Figures 1D, 2, 3). Type: México, Yucatán, Municipio
Valladolid, 680-700 m al E del poblado de Chan Yokdzonot 2, unos 1,380-1,400 m al este del desvío Valladolid-Chan
Yokdzonot, unos 3.7-4 km al norte en línea recta de Valladolid, 20° 44’ 15.34” N, 88° 11’ 23.46” W, 25 m; “ … tre-
padora con hojas unifolioladas y peciolo alado. Frutos delgados, color café-rojizo; las ores enteramente blanco-am-
arillento”, 9 junio 2022, G. Carnevali, R. Duno & M.A. Caamal-Dzul 9395 (holotype: CICY; isotypes: MEXU, MO).
Diagnosis. A species of Centrosema similar to C. sagittatum but with entirely pale cream-yellow owers lacking
nectar guides or any other colored pattern on the banner, with smaller, ovate (vs. elliptic-oblong) bracteoles as-
sociated with each ower. Furthermore, the overall size of the ower is smaller (25-26 vs. 22-46 mm) where the
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Figure 2. Morphology of Centrosema avescens. A. leaves. B. leaves and ower. C. ower, lateral view, showing the close banner. D. owers, front view.
E. calyx and bracteole. F- G. keel and wing, lateral view. H. stamens. (Photos: A-H. Germán Carnevali).
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banner is reduced in size (24-26 vs. 21-58 mm long) and the calyx and its tube are proportionally longer than in C.
sagittatum.
Description. Vine, perennial, to 10 m long. Stem terete, green becoming brown, lenticels present, glabrous. Leaves
(6-)8.0-18 × (2.5-)4.0-8.8 cm, consisting in a sagittate single foliole of an ontogenetically 3-foliolate leaf (by
abortion of lateral folioles), underside pale green, upperside darker, petiole 1.5-40 mm long, winged, thickening
toward the apex, 1.5-4.0 mm wide; stipules setiform, triangular, persistent, 3.0-3.2 mm long, 0.5-0.6 mm broad,
5-6-veined, apex acute, base without basal appendages; stipels at the apex of petiole 0.01-0.02 mm long; apex
acute, basal, retrorse lobules 2.3-4.5 cm long, the internal margin, 2.4-3.8 cm at its widest, sinus slightly curved,
2.2-6 cm across the spread apices of the lobes, rounded, penninerved, bearing 4-6 secondary veins, abaxial surface
glabrous, adaxial surface glabrous with a few diminute hairs along the main vein; apex narrowly acute. Inores-
cences pseudoracemes, each raceme 1-2(-3)-owered, sometimes with one abortive ower; peduncle quadrangular,
pubescent, 15-35 mm long, dull brown, one pair of bracts at the apex of the peduncle, diminute, pedicel 6-7 mm
long, pale green, each ower subtended by two bracteoles 3.5-6.0 × 2.2-3 mm, ovate, acute, base slightly cordate,
multinervate, abaxial and adaxial surface glabrous. Flowers resupinate, showy, pale cream-yellow without colored
nectar guides on the banner, 2.5–2.6 cm long; calyx of 5 sepals, 15-16 × 6-11 mm, tube 9-10 mm long, 9-10 mm
wide, minutely indumented, lobes unequal, triangular, upper (carinal) lobe 3-5.5 × 2-3.0 mm, two laterals 2.5 ×
1.5 mm, lower (vexillary) lobes 1 mm long; corolla consisting of a banner 24-26 × 22-27 mm, orbicular, minutely
indumented along margins and on the adaxial face, base 5 mm long, the dorsal spur 1 mm long; the wings 20 × 5-8
mm, sigmoid, base 2-4 mm long, spur 3 mm long, the reminder distal portion 15 mm long, abaxial face minutely
Figure 3. Distribution of Centrosema avescens (red circles) in the Yucatan Peninsula, and C. sagittatum (black circles) in tropical America. Map created
using the Free and Open Source QGIS (www.qgis.org). The occurrences of Centrosema sagittatum from the Global Biodiversity Information Facility
(GBIF, www.gbif.org).
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indumented, adaxial surface glabrous; keel 16 × 18 mm, the base 4 mm long, the rudimentary claw 1 mm long, the
abaxial margins 12 mm long, both faces glabrous; androecium with 10 stamens, the central one running along the
banner, laments incurved plus anthers 24-28 mm long, irregularly U-shaped, proximally fused for 20 mm, free
portion 3-4 mm long, anthers ca. 1 mm long to oblong, oblong-elliptic, basixed; nectary disc cylindrical, not
lobed. Gynoecium 27-30 mm long, ovary 10 × 1 mm, cylindrical, glabrous, 20 mm long, stigma capitate. Legume
elastically dehiscent, generally one per inorescence, linear, straight or falcate, plano-compressed, 12 × 0.6 cm,
pedicel 1.0 cm long, apex rostrate, rostrum little to well developed, up to 1.5 cm long, margins thickened; valves
leathery, puberulent to glabrous. Seeds 8-10 per pod, not compressed, oblong-ellipsoid; brown, most often with
patches of a lighter color dark; hilum short, oblong to circular.
Distribution and ecology. Campeche, Quintana Roo, and Yucatan (Mexico). Endemic to Mexico where it seems
to be restricted to the Yucatan Peninsula (Figure 3). It grows in lowland (10-100 m asl), seasonally dry forests. All
specimens of Centrosema avescens seen by the authors grow in the margins of partially undisturbed forests and the
owers are always presented low on the plants, under shady conditions. The totally pale cream-yellow owers are
presumably an adaptation to the reection of the low levels of sunlight that reach the understory of the forests. At this
time, it is unknown whether the owers of this species feature ultraviolet nectar guides, in lieu of colored ones. In the
Yucatan Peninsula all the other species of Centrosema grow primarily in secondary vegetation associate to seasonally
dry forests, most commonly directly exposed to sunlight.
A botanical sample from the Municipality of Teapa in the state of Tabasco (H. M. Medina 16, MEXU) has a
unifoliolate leaves with a sagittate blade, and winged petioles. This plant resembles Centrosema avescens and C.
sagittatum, but this particular specimen was collected in sterile condition and it is impossible at this time to ascertain
whether it represents either species. Also, this plant grows in more humid, riparian forests.
In Mexico, Centrosema sagittatum, the putative sister species, grows in Chiapas, Guerrero, Hidalgo, Jalisco, Mi-
choacán, Nayarit, Nuevo León, Oaxaca, Puebla, Sinaloa, Tabasco, Tamaulipas y Veracruz (partially Figure 3). Else-
where, it grows in Central America (Guatemala, Belize, El Salvador, Honduras, Nicaragua, Costa Rica, Panama),
South America (Colombia, Venezuela, Brazil, Bolivia, Paraguay, Argentina), and the Antilles. In the Yucatan Penin-
sula there are nine species of Centrosema (see key, Figure 1).
Conservation Status. The GeoCAT tool (Bachman et al. 2011) estimated the Extent of Occurrence (EOO) of Cen-
trosema avescens as 43,848.885 km2, and its Area of Occupancy (AOO) as 28 km2, based on cells of 2 × 2 km.
Following the IUCN (2012) criteria, the EOO and AOO results place C. avescens in the Near Threatened (NT) and
Endangered (EN) categories, respectively. Because the species is rare, its AOO is small, the species only occurs natu-
rally in nearly undisturbed vegetation, and most of its known populations occur in areas where the original vegetation
is currently being transformed or is likely to be substituted by anthropogenic ecosystems during the next few years
or decades, we propose the species to be treated as Endangered (EN).
Phenology. Centrosema avescens owers June to February, and sets fruits in April to June. On the other hand,
throughout its distribution C. sagittatum has been recorded in ower and/or fruit all the year excepting August and
September whereas Mexican populations of the species have been collected in anthesis October through January.
Etymology. The specic epithet “avescens” refers to the color of the ower, a pale cream yellow.
Common name. Buy-ak’ (maya) (A. Ankli 128).
Additional specimens examined. MEXICO. Campeche. Municipio Campeche, 15 km E of Campeche, 19° 48´
30” N, 90° 22´ 10” W, 4 March 1980, C. D. Johnson 1660-80 (CICY); Municipio Candelaria, 3.5 km al sureste de
Miguel Hidalgo, 17° 51´ 38” N, 90° 49´ 31” W, 30 October 2002, C. Gutiérrez Báez 7572 (CICY, MEXU, UCAM).
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Quintana Roo. Municipio Felipe Carrillo Puerto, Xeret, km 30 carretera Chetumal, 19° 34´ N, 88° 02´ W, 05 May
1986, J. S. Flores 10862 (UADY). Yucatán. Municipio de Tixcacalcupul, Ekpedz, 20° 18´ 55” N, 88° 25´46” W, 28
January 1995, A. Ankli 128 (CICY, MEXU); Municipio Peto, Utziná, 19° 52’ 03” N, 88° 59’ W, 19 November 1992,
G. Campos 2988 (CICY); Municipio de Yaxcabá, Yaxcabá, 20° 33´ N, 88° 49´ W, 30 April 1986, D. Zizumbo & P.
Sima 278 (CICY).
Discussion
Originally this population was considered an albino form of Centrosema sagittatum. Later we realized that this
character state is recurrent in all specimens and populations of Centrosema with unifoliolate, sagittate leaves and
winged petioles (features of C. sagittatum) growing in the Yucatan Peninsula, and that there were at least six other
localities in the states of Campeche, Quintana Roo, and Yucatan. In general, the owers of Centrosema species
show a color pattern where there is a difference, often dramatic, between the overall ower color and the nectar
guides (or macula) of the banner. As a rule, species with lavender, lilac, or mauve ower color (colors 43, 44, 46,
Graf 1966) have white nectar guides, whereas predominantly white or pale yellowish owers display cherry, blood
red or cardinal red (colors 26, 27, and 28, Graf 1966) nectar guides. Centrosema avescens is the only known spe-
cies with an entirely pale cream-yellow ower in Mexico (color 1, Graf 1966) lacking nectar guides reecting in
the visible spectrum. Furthermore, in this new species the pair of bracteoles associated with each ower are smaller
and ovate (vs. elliptic-oblong), the general size of the ower is smaller (25-26 vs. 22-46 mm long) and the same is
true of the banner (24-26 vs. 21-58 mm long). Also, the calyx and its tube are longer in C. avescens as compared
with C. sagittatum (Table 1).
It would be always possible to consider this taxon as a subspecies of Centrosema sagittatum, differing in col-
oration of the ower, some morphological differences and the geographical isolation but we believe these Yucatan
Peninsula populations are quite distinctive from C. sagittatum and other unifoliolate species from South America.
C. avescens C. sagittatum (1) C. sagittatum (2)
Bracteole (mm) 3.5-6.0 × 2.2-3 4.5-10 × 2-5 7-9 × 5-7
Bracteole, shape Ovate Elliptic-oblongate -
Flower length (cm) 2.5-2.6 2.2-4.8 2.5-4
Calyx size (mm) 15-16 × 6-11 7-13.5 -
Tube calyx length (mm) 9-10 5-7 5-6
Calyx lobes, length (mm) 3-5.5 3-7 4-6
Calyx lobes, wide (mm) 2-3.0 - -
Banner, color Pale cream-yellow
without nectar guides
White with purple
nectar guides
White with purple
nectar guides
Banner, length (mm) 24-26 21-58 -
Banner, wide (mm) 22-27 17-32 -
Wings, length (mm) 20 20-24 -
Wings, wide (mm) 5-8 - -
Table 1. Distinguishing characters of Centrosema avescens and C. sagittatum.
Character states from Barreto et al. 2020 (1) and Fantz 1993 (2)
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Key to the species of Centrosema in the Yucatan Peninsula
(C. sagittatum included for comparison)
1. Leaves 1-foliolate, rarely 3-foliolate but only in the base of the plant .....................................................................2
1. Leaves always 3-foliolate ….....................................................................................................................................3
2. Petioles lacking wings; leaets linear to narrowly oblong; owers purple or lavender …….Centrosema unifoliatum
2. Petioles winged; leaets sagittate; owers entirely pale cream-yellow, white with purple center or completely
white ..……………………………………………..................................................................................................3
3. Bracteole 3.5-6.0 × 2.2-3 mm, ovate; calyx 15-16 × 6-11 mm; tube 9-10 mm long; banner 24-26 × 20-27 mm, pale
cream-yellow, lacking nectar guides…..…...….……........................................................... Centrosema avescens
3. Bracteole 4.5-10 × 2-5, elliptic-oblongate; calyx 7-13.5 mm long, tube 5-7 mm long; banner 21-58 × 17-32 mm,
white or yellowish with purple nectar guides...……..............................................................Centrosema sagittatum
4. Ventral calyx lobes subequal to the other four teeth or inconspicuous…………......................................................5
4. Ventral calyx lobes longer than the other four teeth ..................................................................................................6
5. Leaets linear; owers purplish to violet with white center, 1-1.5 cm long; fruits 5.5-7 × 3-4 mm…………….……
…………………………….………………….…................................................................Centrosema pascuorum
5. Leaets elliptic-ovate, narrowly oblong, or rarely linear; owers lavender with white center, 2.5-3.5(4) cm long;
fruits 8-13 × 3-5 mm……………….………………..........................................................Centrosema virginianum
6. Petiolules nearly absent, to 3 mm long; leaets typically linear to narrowly oblong, no more than 0.5 cm wide........
.........................................................................................................................................Centrosema angustifolium
6. Petiolules conspicuously longer than 3 mm long; leaets more than 1.5 cm wide, ovate, ovate-rhombic, elliptic,
sometimes pandurate ...............................................................................................................................................7
7. Leaets rhombic-ovate, basally asymmetric; ventral calyx lobes 1-2 mm long .......................................................8
7. Leaets elliptic to ovate or elliptic-lanceolate, basally symmetric; ventral calyx tooth more than 2.5 mm long…9
8. Petiolules 5-6 mm long; leaets ovate to rhombic-ovate, often blackish when dried; owers white with purple ban-
ner center, 3.5-5 cm long; fruits 8-12 mm wide…….................................................................Centrosema plumieri
8. Petiolules 3-4 mm long; leaets generally pandurate, leaves not blackish when dried; owers violet to purplish-red
with white nectar guides, 2.5-3 cm long; fruits 9-16.5 mm wide ……......................................Centrosema schottii
9. Bracteoles 10-15 mm long; owers white fading dull yellowish, maroon medially and along veins, 3-3.5 cm long;
fruits 10-19 cm long, rostrum 12-18 mm long…..............................................................Centrosema macrocarpum
9. Bracteoles 6-11 mm long; owers pale purple with pale-yellow to white nectar guides, 2-3 cm long; fruits (6.5-)10-
14 cm long, rostrum 5-12 mm long ..................................................................................................Centrosema molle
Acknowledgements
Authors are grateful to Silvia Hernández, Lilia Lorena Can, and Nestor Raigoza for help in the management of her-
barium material. We are indebted to Miguel Ángel Caamal who led two of the authors (GC & RD) to the type locality
of Centrosema avescens and showed us this plant for the rst time. Finally, Gustavo Romero, Edgar Ramón Gómez
Vega and Alfredo Dorantes Euán who kindly gave us permission to use their digital photos.
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Associate editor: Martha Juana Martínez Gordillo
Author contributions: GC, eld work, specimen examination, analysis of data, and writing of manuscript drafts; DA, specimen examination,
mapping, data analysis, and writing of manuscript drafts; JLT analysis of data, and writing of manuscript drafts; IR, writing of the manuscript,
and analysis; RD, eld work, specimens examination, analysis of data, and writing of manuscript drafts.
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