Phytotaxa 649 (1): 111–120 ISSN 1179-3155 (print edition)

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Article PHYTOTAXA
Copyright © 2024 Magnolia Press ISSN 1179-3163 (online edition)

https://doi.org/10.11646/phytotaxa.649.1.7

A new species of Polystemma (Apocynaceae, Asclepiadoideae, Asclepiadeae,

Gonolobineae) from the state of Oaxaca, Mexico
LEONARDO O. ALVARADO-CÁRDENAS1,3*, ABISAÍ JOSUÉ GARCÍA-MENDOZA2,4, DANIEL SANDOVAL-
GUTIÉRREZ2,5 & LUCIO LOZADA-PÉREZ1,6
¹Departamento de Biología Comparada, Laboratorio de Plantas Vasculares, Facultad de Ciencias, Universidad Nacional Autónoma de
México, Apartado Postal 70-282, 04510, Ciudad de México, México
2
Universidad Nacional Autónoma de México, Instituto de Biología, Jardín Botánico. Tercer circuito exterior de Ciudad Universitaria,
Coyoacán, 04510 Ciudad de México, México
3�
leonardoac@ciencias.unam.mx; https://orcid.org/0000-0002-4938-8339
4�
abisai@ib.unam.mx; https://orcid.org/0000-0002-0284-5117
5�
sagudan2@hotmail.com; https://orcid.org/0000-0002-5141-5906
6�
lope@ciencias.unam.mx; https://orcid.org/0000-0003-1093-5830
Corresponding author: � leonardoac@ciencias.unam.mx

Abstract

We describe a new species of Polystemma endemic to Oaxaca, Mexico. Polystemma leopardum is similar to P. cordatum
but differs in the shape of the corolla lobes, flower color pattern, shape of the gynostegial corona and stylar head, as well as
its specialized habitat. We describe and discuss its morphology and provide illustrations and a distribution map. We propose
its conservation status as Endangered under the criteria of the IUCN. This discovery increases the diversity of the genus in
the country to ten species.

Key words: Biodiversity, Endemic species, Flora of Oaxaca, Gentianales, gypsophylic

Introduction

Polystemma Decaisne (1844: 602) is a genus of the family Apocynaceae endemic to the American continent and
distributed from Mexico to Costa Rica (Stevens 2009; Morillo 2023). The habit of these plants is mainly climbing
(shrubby in P. fishbeiniana V.W. Steinmann & W.D. Stevens (2022: 760)). They have suberous stems when mature and a
morphologically diverse gynostegium. The following combination of characters allows the recognition of the members
of this taxon: mixed, simple, and glandular trichomes, the later white and becoming clear with age; gynostegial corona
fused into a ciatiform structure with the margin fimbriate, crenulate, dentate, or subentire, and slightly 5-lobate, with
follicles fusiform, smooth and mottled (Stevens 2000, 2001, 2005; Steinmann & Stevens 2022; Morillo 2023).
Phylogenetic studies based on molecular data recover Polystemma sensu Stevens as a monophyletic group included
within the paraphyletic genus Matelea Aublet (1775: 277) sensu Woodson (1941), whose subgeneric classification
is recognized as artificial (Krings et al. 2008; McDonnell et al. 2018). In the current classification for the family,
Polystemma is accepted as a distinct taxon (Endress et al. 2018); in addition, there have been some recent nomenclature
changes from Matelea to Polystemma (Alvarado-Cárdenas et al. 2020, 2021; Morillo 2023), and new species have
been described (McDonnell & Fishbein 2016; Steinmann & Stevens 2022).
Currently, the group includes ten species (Steinmann & Stevens 2022; Morillo 2023, Table 1), but it has been
suggested that it could contain around 20 species (Stevens 2009; McDonnell & Fishbein 2016; Hernández Barón
2021). However, there are still species that have not been transferred to the genus or are undescribed. Therefore, the
delimitation of Polystemma is still under development.
During fieldwork performed from 2017 to 2022 for the generation of a floristic inventory of San Juan Teita,
Oaxaca, Mexico (in-progress), we collected plants that were initially identified as Polystemma cordatum (Brandegee
1908: 252) L.O. Alvarado (2021: 12), a species endemic to the Tehuacán-Cuicatlán Valley of Puebla and Oaxaca,
Mexico (Juárez-Jaimes & Lozada-Pérez 2003). However, detailed observation of the morphology of this plant allowed

Accepted by Michele Rodda: 27 Apr. 2024; published: 16 May 2024 111

its recognition as a new species. In this work, we considered it necessary to include an illustration and description of
the taxon, as well as an assessment of its risk category.

TABLE 1. Species list of Polystemma and their distribution. Names with an asterisk are endemic to Mexico.
Species name Distribution

1. *Polystemma calcicola (Greenm.) Morillo Mexico: Guerrero, Morelos, Oaxaca.

2. *Polystemma canisferum McDonnell & Fishbein Mexico: Sonora.

3. Polystemma cordifolium (A. Gray) McDonnell & Fishbein Mexico: Baja California, Baja California Sur, Chihuahua, Sinaloa, Sonora.
United States of America: Arizona.

4. *Polystemma cordatum (Brandegee) L.O. Alvarado Mexico: Oaxaca, Puebla.

5. *Polystemma fishbeiniana V.W. Steinm. & W.D. Stevens Mexico: Michoacan.

6. Polystemma guatemalense (Schltr.) W.D. Stevens Costa Rica: Alajuela, Guanacaste, Punta Arenas.
El Salvador: Ahuachapan, Cabañas, Chalatena, La Libertad, La Union, San
Salvador, San Vicente, Santa Ana, Sonsonate, Usulutan.
Guatemala: Baja Verapaz, Chiquimula, El Progreso, Guatemala,
Huehuetenango, Jutiapa.
Honduras: Choluteca, Comayagua, El Paraíso, Francisco Morazan, La Paz.
Mexico: Chiapas, Colima, Guerrero, Jalisco, Mexico, Michoacan, Morelos,
Nayarit, Oaxaca, Puebla, Sinaloa.
Nicaragua: Boaco, Carazo, Esteli, Granada, Leon, Chinandega, Chontales,
Jinotega, Madriz, Managua, Masaya, Matagalpa, Nueva Segovia, Rivas.

7. *Polystemma leopardum L.O. Alvarado, García-Mend., D. Mexico: Oaxaca.

Sandoval & Lozada-Pérez

8. *Polystemma mirandae Lozada-Pérez Mexico: Guerrero, Oaxaca, Puebla.

9. *Polystemma pilosum (Benth.) Morillo, Mexico: Aguascalientes, Coahuila, Durango, Guanajuato, Hidalgo, Jalisco,
Mexico, Michoacan, Morelos, Nayarit, Nuevo Leon, Oaxaca, Puebla,
Querétaro, San Luis Potosí, Sinaloa, Tamaulipas, Veracruz, Zacatecas.

10. *Polystemma stevensii G.M. Hern.-Barón, Trujillo-Juárez Mexico: Michoacan

& V.W. Steinm.

11. Polystemma viridiflorum Decne. El Salvador: La Union.

Guatemala: Chiquimula, El Progreso, Zacapa.
Honduras: Choluteca, El Paraiso.
Mexico: Chiapas, Guerrero, Morelos, Oaxaca, Puebla, Veracruz.

Materials and methods

The specimens of the new taxon proposed herein were processed following standard methods (Lot & Chiang 1986).
Later, the material was compared to related taxa by examining specimens deposited in the following herbaria: ENCB,
FCME, HUAA, HUAP, MEXU, and UAMIZ (acronyms follow Thiers 2022), as well as the descriptions of species of
the genus in nearby states or in available floras.
The description was based on the evaluation of characters from dried material. The morphological measurements
were obtained using a digital caliper (Simhevn/Digital Caliper). The measurements and details of the trichomes, as

112 • Phytotaxa 649 (1) © 2024 Magnolia Press ALVARADO-CÁRDENAS et al.

well as the floral structures, were obtained under a Nikon stereomicroscope (C-Leds, SMZ445, Tokyo, Japan). The
descriptions were based on Hickey (1973) for the leaves, Harris and Harris (1994) for the indumentum, and Stevens
(2009) for the corona. A table comparing the species examined is provided.
The conservation status of the new species was evaluated using the criteria of the IUCN Red List (2019). We
calculated the area of occupation of the species (AOO) using the program Geocat (Bachman & Moat 2012), and the
final risk category was assessed based on ecological information and field observations.
Proposed taxa (species, genera, families, etc.) are essentially explanatory hypotheses based on abductive
reasoning. The construction of explanatory hypotheses requires framework knowledge and theory that are expected to
be observed under plausible causal conditions, as well as observations that require explanation (Fitzhugh 2005, 2013).
The base knowledge utilized here for the species hypothesis is the cohesive species concept of Templeton (1989), in
conjunction with our observations of morphology and distribution. The cohesive species concept is based on population
genetics, but it does not exclude the possibility that other cohesive factors explain the similarity among organisms that
conform the species hypothesis. For example, the expression of morphology (limitations of the phenotypic variability
of individuals) contribute evidence of the tokogenetic relationships among individuals that share similar attributes that
are not shared by individuals associated with other hypotheses (i.e., other taxa). These morphological attributes arise
among members of an ancestral population through some unspecified evolutionary process (natural selection, genetic
drift, self-organization, etc.) and are fixed among the members of the current populations over time. At the same time,
the distinctive character of the habitat (geographic distribution, ecological limitations) could play an important role in
restricting the distribution of the individuals of the population and keeping them separate from the individuals of other
species. Here, we use these two factors to include in the hypothesis and name the individuals as a species. In the present
work, when we refer to taxa or species, we are referring to the individuals associated with the corresponding explanatory
hypothesis. In addition, the proposed name for the new species follows the current version of the International Code of
Nomenclature for Algae, Fungi, and Plants (Turland et al. 2018).

Results

Polystemma leopardum L.O. Alvarado, García-Mend., D. Sandoval & Lozada-Pérez sp. nov. (Figures 1–4).

Diagnosis. Species similar to Polystemma cordatum in having campanulate flowers with long trichomes on the corolla lobes and similar
corona appendages; Polystemma leopardum differs by its yellowish flowers with a reticulate purple to black pattern, ovate-lanceolate
corolla lobes, internal gynostegial corona with four small teeth between and below the linear-lanceolate appendages, and a convex
stylar head (vs. red flowers with a reticulate black pattern, internal gynostegial corona with zero, one or two teeth between the linear-
lanceolate appendages and flat stylar head in P. cordatum).
Type:—MEXICO. Oaxaca: Distrito Tlaxiaco, Municipio San Juan Teita, 200 m al E de San Juan Teita, cerro del Panteón 1466 m,
17°05’32.51’’N, 97°24’33.59’’W, 8 August 2022, D. Sandoval-Gutiérrez & C. Flores-Fausto 1547 (holotype: MEXU, isotypes: IEB,
FCME, MEXU, MO, OAX, to be distributed).

Twining plants with white latex. Stems becoming suberous with age, cylindrical with a mixed indumentum of short
simple and glandular trichomes densely pubescent, large simple trichomes sparsely pubescent. Leaves opposite, petiole
2.5–3.5 cm long, with indumentum similar to the stem; leaf blade 3–5.5 × 2–3.8 cm, ovate, apex acute to broadly
acuminate, base cordate, lobes 3.3–5.3 × 7–14 mm, sparsely to densely pubescent adaxially, glandular trichomes
absent, densely pubescent mainly on the midveins and secondary veins abaxially; colleters at the base of the midvein
adaxially, 4–6. Inflorescences extra-axillary, one per node, racemiform; peduncle 2–3.9 cm long, with indumentum
similar to the stem; bracts 4–6.6 × 0.9–1 mm, linear to lanceolate; pedicel 1.4–2.3 cm long. Calyx green, 5-lobulate,
lobes 7–8 × 2–3 mm, lanceolate to elliptic–lanceolate, densely pubescent abaxially. Corolla campanulate, 2–2.5 cm in
diameter, yellowish with black or dark purple coloration in the tube, with a reticulate pattern on the lobes, tube 4.9–6
mm long, lobes 5–8.2 × 5–6.8 mm, ovate-lanceolate, apex acute, barbate adaxially, with eglandular trichomes 2.5–3.0
mm long; gynostegial corona adnate at the union of the gynostegium and corolla; external corona dark yellow to
yellowish at the base, dark purple to black towards the tip, formed by 5 lobes opposite to the anthers, fused laterally,
each lobe with two apical, linear-lanceolate appendages 2.0–2.6 mm long, and 1–2 (3) teeth 0.2–0.3 mm long between
them and sometimes below them, internal corona with two digitate appendages 0.8–1 mm long, with (2) 4 small teeth
ca 0.1 mm long between them, gynostegium with a stipe 0.8–1.1 mm long, style apex convex, obtuse, dark purple to

A new Polystemma for Mexico Phytotaxa 649 (1) © 2024 Magnolia Press • 113
black. Pollinarium with a brown corpuscle, elliptical, pollinia ellipsoid, laterally excavated. Follicles fusiform, 12–15
× 1–1.5 cm, glabrous. Seeds not seen. Figures 1–2.

FIGURE 1. Polystemma leopardum A. Branch segment with inflorescence and flower bud. B. Detail of stem
pubescence. C. Detail of leaf base with colleters. D. Flower. E. Gynostegium and gynostegial corona. F. Detail of
the lobe of the gynostegial corona G. Pollinarium. H. Fruit. Illustration by Ericka Belén Cortez Castro, based on the
holotype.

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FIGURE 2. Polystemma leopardum A. Habitat. B. Plant climbing. C. Detail of suberous stem. D. Leaves and flowers.
E. Top view of flower and bud. F. Lateral view of flower. G. Gynostegium and gynostegial corona. H. Fruit. Photograph
credits A–F Abisaí García-Mendoza, G–H Abigail López Santiago.

Distribution and habitat. Polystemma leopardum is known only from the municipality of San Juan Teita, Tlaxiaco
district, Oaxaca, Mexico (Fig. 3). The plants grow on rocky slopes with gypsic soils, at elevations of 1323–1466 m. It
inhabits xerophytic scrub and tropical deciduous forest with Agave gypsicola García-Mend. & D.Sandoval in García-
Mendoza et al. (2019: 6), Calochortus multicolor García-Mend., D.Sandoval & Chávez-Rendón in García-Mendoza et
al. (2023: 3), Cephalocereus parvispinus Arias, Tapia & Guzmán (2019: 150), Mixtecalia teitaensis García-Mendoza,
D.Sandoval & Redonda-Martínez (2020: 128), Sisyrinchium longispathum Conzatti (1947: 124), and Xochiquetzallia
magnifolia García-Mendoza & Gutiérrez (2022: 202).

A new Polystemma for Mexico Phytotaxa 649 (1) © 2024 Magnolia Press • 115
FIGURE 3. Known geographical distributions of Polystemma cordatum and P. leopardum.

Phenology. Flowering and fruiting are known from June to October.

Conservation status. Individuals are known from only five populations (Fig. 3), such that the area of occupation
(AOO) is 8 km2. It is found in a specialized habitat with gypsic soils, which is affected by livestock grazing similarly
to reports in Agave gypsicola García-Mend. & D. Sandoval (2019: 6-9) (García-Mendoza et al. 2019). Considering
that the known distribution is very restricted, with only five populations recorded, and given the anthropogenic impact
affecting the habitat, We therefore propose the new species in the category of Endangered (B2abiii).
Etymology. The specific epithet refers to the pattern of yellow coloration with black tones reminiscent of the
coloration of the ocelot (Leopardus pardalis Linnaeus 1758: 42), a feline distributed from the southern United States
to northern Argentina.
Additional specimens examined:—MEXICO: Oaxaca, distrito Tlaxiaco: municipio San Juan Teita, 1 km
NE de San Juan Teita, 1,346 m, 17°05’46.41’’N, 97°24’44.92’’W, 8 August 2019, A. García-Mendoza et al. 11412
(MEXU); Kava xikití [Peña de espalda delgada], 1 km SE de San Juan Teita, 1,350 m, 17°5’48.26’’N, 97°24’43.7’’W,
10 June 2018, A. López Santiago & I. Santiago-Cruz. 149 (MEXU); Ladoxuu 1 km E de San Juan Teita, 1,323 m,
17°05’48.26’’N, 97°24’44.2’’W, 28 August 2019, A. López Santiago & I. Santiago-Cruz 555 (MEXU); Tiko ‘do ñuu, 2
km E de San Juan Teita, 1,353 m, 17°05’48.11’’N, 97°24’44.02’’W, 1 October 2019, A. López Santiago & I. Santiago-
Cruz 571 (MEXU).
Taxonomic remarks. The species proposed here shares the attributes of the genus Polystemma and is distinguished
from the rest of the species by its flowers, which present a distinct pattern of coloration within the group (Fig. 1–2).
The recognition of this new taxon increases the number of species for the country to eleven (Table 1) with an endemism
of 75 %. These results reaffirm the country as the center of diversity for the genus and family. Polystemma cordatum is
the species with the strongest similarity to the species proposed here (Fig. 4), which differs in the coloration and size
of the flower as well as the shape of the gynostegial corona and the stylar head (Juárez-Jaimes & Lozada-Pérez 2003),
(Table 2). This morphological difference between the individuals of the two species hypotheses is consistent with the
proposed phenotypic restriction laid out in the explanatory hypothesis.

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FIGURE 4. Morphologically similar species. A–D. Polystemma cordatum. A. Branch with flowers of the type. B–C.
Different views of the flowers of the type. D. Detail of the gynostegium. E–H. Polystemma leopardum. E. Branch with
flowers of the type. F. Detail of the gynostegium. G. Section of the flower. H. Detail of the gynostegium. Photograph
credits: A–C Holotype specimen, Purpus 3836 (UC124986!), D. Illustration by Elvia Esparza, Flora de Tehuacán-
Cuicatlán (Juárez-Jaimes & Lozada 2003), E–G. Specimen type H. Illustration by Ericka Belén Cortez Castro, based
on the holotype.

A new Polystemma for Mexico Phytotaxa 649 (1) © 2024 Magnolia Press • 117
TABLE 2. Morphological attributes present in the compared Polystemma species.
Polystemma cordatum Polystemma leopardum
Bracts 2–3 mm long 4–6.6 mm long
Flower diameter 2–2.5 cm 2–2.5 cm
Tube 4.5 mm long, dark red 4.9–6 mm long, black or dark purple
5–8.2 × 5–6.8 mm, ovate-lanceolate, yellowish with
Lobes 6–7 × 5–5.5 mm, ovate, dark red
black or dark purple reticulated pattern
bilobed, 1.5 mm long, without small teeth bilobed, 2.0–2.6 mm long, with small teeth between
External corona
between them them and sometimes below them
Internal corona bilobed with 0–2 small teeth between them bilobed with (2) 4 small teeth between them
Style apex flat convex, obtuse

Unlike Polystemma cordatum, which is distributed in calcic soils, the new species is strictly gypsophilic, similar
to other species described in the zone, such as Agave gypsicola, Cephalocereus parvispinus, Mixtecalia teitaensis
and Xochiquetzallia magnifolia (Arias-Montes et al. 2019; García-Mendoza et al. 2019, 2023; García-Mendoza &
Gutiérrez 2022). According to Ortiz-Brunel et al. (2023), Polystemma leopardum represents the first record in the
family Apocynaceae of a strictly gypsophilous species for Mexico, such that it also represents an advancement of
the knowledge of the species of this genus in the country. Finally, this discovery corroborates the need to establish
strategies for the conservation of this edaphic assemblage, which contains numerous species of irreplaceable character
in the state.

Acknowledgements

We thank the municipal authorities and the Comisariado de Bienes Comunales de San Juan Teita for allowing us to
carry out the floristic inventory of the municipality, as well as Abigail López Santiago and César Flores Fausto for
their efficient support in the collection and herborization of specimens; Sofía Islas-Hernández for observations that
improved the manuscript; María Eugenia Muñiz Díaz de León for technical support in the Plant Biology Workshop 1
and 2; Ericka Belén Cortez Castro for the excellent illustration; the curators and technicians of the herbaria visited for
their help providing access to the herbarium specimens; Rosalinda Medina Lemos, editor-in-chief of the Flora del Valle
de Tehuacán Cuicatlán, for allowing us to use the illustration of the gynostegium of the species Polystemma cordatum;
and Lynna Kiere for her translation services for this manuscript. This work is part of the MSc thesis of DSG. (CVU
779565). Thank the Posgrado en Ciencias Biológicas, UNAM, and are supported by a grant from the Consejo Nacional
de Humanidades, Ciencias y Tecnologías (CONAHCYT).

References

Alvarado-Cárdenas, L.O., Lozada-Pérez, L., Islas-Hernández, S.C., Cortez, E.B., Maya-Mandujano, K.G. & Chávez-Hernández, M.G.
(2020) Apocináceas de ayer y hoy. Conocimiento histórico y reevaluación de la diversidad y distribución de Apocynaceae en México.
Botanical Sciences 98 (2): 393–416.
https://doi.org/10.17129/botsci.2525
Alvarado-Cárdenas, L.O., Chávez-Hernández, M.G. & Velazco-Macías, C.G. (2021) Ajustes taxonómicos en Apocynaceae Mexicanas.
Phytoneuron 47: 1–22.
Arias, S., Tapia, H.J. & Guzmán, U. (2019) A new species of Cephalocereus (Cactaceae) from southern Mexico. Phytotaxa 392 (2):
147–156.
https://doi.org/10.11646/phytotaxa.392.2.4
Aublet, J.B.C.F. (1775) Histoire des Plantes de la Guiane Françoise. Libraire de la Faculté de Médecine, London & Paris, 621 pp.
Bachman, S. & Moat, J. (2012) GeoCAT: an open source tool for rapid red list assessments. BGjournal 9 (1): 11–13. [https://www.jstor.
org/stable/24811237]
Brandegee, T.S. (1908) New species of Mexican plants. Zoe 5 (11): 244–262.
Conzatti, C. (1947) Flora Taxonómica Mexicana. Vol. 2. Sociedad Mexicana de Historia Natural, Mexico City, pp. 1–220.

118 • Phytotaxa 649 (1) © 2024 Magnolia Press ALVARADO-CÁRDENAS et al.

Decaisne, J. (1844) Asclepiadeae. In: De Candolle, A.P. (Ed.) Prodromus Systematis Naturalis Regni Vegetabilis, Vol. 8. Paris, Masson,
pp. 490–665.
Endress, M.E., Meve, U., Middleton, D.J. & Liede-Schumann, S. (2018) Apocynaceae. In: Kadereit, J.W. & Bittrich, V. (Eds.) Flowering
Plants. Eudicots, The Families and Genera of Vascular Plants 15. Springer International Publishing AG, pp. 207–411.
https://doi.org/10.1007/978-3-319-93605-5_3
Fitzhugh, K. (2005) The inferential basis of species hypotheses: the solution to defining the term ‘species’. Marine Ecology 26 (3‐4):
155–165.
https://doi.org/10.1111/j.1439-0485.2005.00058.x
Fitzhugh, K. (2013) Defining ‘species’,‘biodiversity’, and ‘conservation’by their transitive relations. In: Pavlinov, I.Y. (Ed.) The Species
Problem-Ongoing Problems. New York: InTech. pp. 93–130.
https://doi.org/10.5772/52331
García-Mendoza, A.J., Franco-Martínez, I.S. & Sandoval-Gutiérrez, D. (2019) Cuatro especies nuevas de Agave (Asparagaceae,
Agavoideae) del sur de México. Acta Botanica Mexicana 126: e1461.
https://doi.org/10.21829/abm126.2019.1461
García-Mendoza, A.J., Sandoval-Gutiérrez, D. & Redonda-Martínez, R. (2020) Mixtecalia, a new monotypic genus of the subtribe
Tussilagininae (Senecioneae, Asteraceae) from the state of Oaxaca, Mexico. Phytotaxa 438 (2): 119–129.
https://doi.org/10.11646/phytotaxa.438.2.5
García-Mendoza, A.J. & Gutiérrez, J. (2022) Xochiquetzallia magnifolia (Asparagaceae, Brodiaeoideae), a new species from Oaxaca,
Mexico. Phytotaxa 552 (3): 201–207.
https://doi.org/10.11646/phytotaxa.552.3.4
García-Mendoza, A.J., Sandoval-Gutiérrez, D. & Chávez-Rendón, C. (2023) Una especie nueva de Calochortus (Liliaceae) de Oaxaca,
México. Acta Botanica Mexicana 130: e2188.
https://doi.org/10.21829/abm130.2023.2188
Harris, J.G. & Harris, M.W. (1994) Plant identification terminology: an illustrated glossary. Spring Lake Publishing, Utah, 216 pp.
Hernández Barón, G.M. (2021) Sistemática del género Polystemma (Gonolobinae, Apocynaceae). MS Thesis. Universidad de Guadalajara,
Guadalajara, 124 p.
Hickey, L.J. (1973) Classification of the architecture of dicotyledonous leaves. American Journal of Botany 60 (1): 17–33.
https://doi.org/10.1002/j.1537-2197.1973.tb10192.x
IUCN (2019) Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions
Subcommittee. Available from: http://www.iucnredlist.org/documents/RedListGuidelines.pdf (accessed 1 April 2023)
Juárez-Jaimes, V.C. & Lozada-Pérez, L. (2003) Asclepiadaceae. In: Medina-Lemus, R. (Ed.) Flora del Valle de Tehuacán-Cuicatlán. Vol.
37. Universidad Nacional Autónoma de México, Instituto de Biología, México, D.F., pp. 1–57.
Lot, A. & Chiang, F. (1986) Manual de Herbario. Administración y Manejo de Colecciones. Técnicas de Recolección y Preparación de
Ejemplares Botánicos. México: Consejo Nacional de la Flora de México. AC., México, pp. 142. [ISBN: 9686144005].
Krings, A., Thomas, D.T. & Xiang, Q. (2008) On the generic circumscription of Gonolobus (Apocynaceae, Asclepiadoideae): Evidence
from molecules and morphology. Systematic Botany 33: 403415.
https://doi.org/10.1600/036364408784571527
Linnaeus, C. (1758) Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis,
synonymis, locis. Editio decima reformata 1758, Impensis direct. Laurentii Salvii (Salvius publ.). Holmiæ, 824 pp.
https://doi.org/10.5962/bhl.title.542
McDonnell, A. & Fishbein, M. (2016) Polystemma canisferum (Apocynaceae, Asclepiadoideae): a distinctive new gonoloboid milkweed
vine from Sonora, Mexico. Phytotaxa 246 (1): 78–84.
https://doi.org/10.11646/phytotaxa.246.1.6
McDonnell, A., Parks, M. & Fishbein, M. (2018) Multilocus Phylogenetics of New World Milkweed Vines (Apocynaceae, Asclepiadoideae,
Gonolobinae). Systematic Botany 43 (1): 77–96.
https://doi.org/10.1600/036364418X697021
Morillo, G. (2023) Aportes al conocimiento de las Gonolobinae (Apocynaceae—Asclepiadoideae). Parte IV. Memoria de la Fundación La
Salle de Ciencias Naturales 81 (190): 45–90. [ISSN: 2443–4698]
Ortiz-Brunel, J.P., Ochoterena, H., Moore, M.J., Aragón-Parada, J., Flores, J., Munguía-Lino, G., Rodríguez, A., Salinas-Rodríguez, M.M.
& Flores-Olvera, H. (2023) Patterns of Richness and Endemism in the Gypsicolous Flora of Mexico. Diversity 15 (4): 1–17.
https://doi.org/10.3390/d15040522
Steinmann, V.W. & Stevens, W.D. (2022) Polystemma fishbeiniana (Apocynaceae, Asclepiadoideae), a new species from the Balsas
Depression of Michoacán, Mexico. Botanical Sciences 100 (3): 759–764.
https://doi.org/10.17129/botsci.2997

A new Polystemma for Mexico Phytotaxa 649 (1) © 2024 Magnolia Press • 119
Stevens, W.D. (2000) New and interesting milkweeds (Apocynaceae, Asclepiadoideae). Novon 10 (3): 242–256.
https://doi.org/10.2307/3393108
Stevens, W.D. (2001) Asclepiadaceae. In: Stevens, W.D., Ulloa, C., Pool, A. & Montiel, O.M. (Eds.) Flora de Nicaragua. Vol. 1. St. Louis:
Missouri Botanical Garden Press, pp. 234–270. [ISBN: 9780915279951]
Stevens, W.D. (2005) New and interesting milkweeds (Apocynaceae, Asclepiadoideae). Novon 15: 602–619.
Stevens, W.D. (2009) Asclepiadaceae. In: Davidse G, Sousa, S.M., Knapp, M. & Chiang, F. & Barrie, F.R. (Eds.) Flora Mesoamericana:
Cucurbitaceae a Polemoniaceae. México: Universidad Nacional Autónoma de México, Instituto de Biología; Saint Louis: Missouri
Botanical Garden; London: The Natural History Museum, pp. 703–768. [ISBN 979-607-02-0901-7].
Templeton, A. (1989) The meaning of species and speciation: A genetic perspective. In: Otte, D. & Endler, J.A. (Eds.) Speciation and its
Consequences. United Estates, Massachusetts: Sinauer Associates, pp. 3–27. [ISBN-13: 978-0878936588].
Thiers, B. (2021) Index Herbariorum: A global directory of public herbaria and associated staff. New York Botanical Garden’s Virtual
Herbarium. Available from: http://sweetgum.nybg.org/science/ih (accessed 2 July 2021).
Turland, N.J., Wiersema, J.H., Barrie, F.R., Greuter, W., Hawksworth, D.L., Herendeen, P.S., Knapp, S., Kusber, W.-H., Li, D.-Z., Marhold,
K., May, T.W., McNeill, J., Monro, A.N., Prado, J., Price, M.J. & Smith, G.F. (2018) International Code of Nomenclature for Algae,
Fungi, and Plants (Shenzhen Code). Adopted by the Nineteenth International Botanical Congress Shenzhen, China, July 2017.
Glashütten, Germany: Koeltz Botanical Books.
https://doi.org/10.12705/Code.2018
Woodson, R.E. (1941) The North American Asclepiadaceae I. Perspective of the genera. Annals of the Missouri Botanical Garden 28 (2):
193–224.
https://doi.org/10.2307/2394270

120 • Phytotaxa 649 (1) © 2024 Magnolia Press ALVARADO-CÁRDENAS et al.