Four new species of Matelea (Apocynaceae: Asclepiadoideae) endemic to Mexico

Four new species of Matelea, endemic to Mexico, are proposed and described: M. balrog, M. cornuta, M. jaimesiae and M. lokii. These taxa differ from each other and M. gonoloboides, M. medusae and M. porphyrantha (the Matelea gonoloboides species complex) in their corolla shapes and gynostegial corona ornamentation. Descriptions, illustrations, morphological comparisons and geographic distributions of these species, as well as their conservation status, are provided. A lectotypification for the name M. gonoloboides is also included. These discoveries highlight Mexico as a centre of diversity and endemism for the genus, with 69 species currently known from the country, of which 66% are restricted to it.

It has been suggested that Matelea s.s.(sensu Krings & Morillo 2015;Morillo 2015;Morillo et al. 2017) comprises around 20 species morphologically consistent with the type species M. palustris Aubl.(Stevens 2001;Krings & Morillo 2015).However, generic circumscriptions are far from settled and several alternative proposals have been suggested, such as Stevens (2009), Morillo (2015) and Endress et al. (2018).We adopted the latter's circumscription of the genera, as it represents a review of the phylogenetic work to date and the most recent proposal for the classification of the entire family.
Matelea has its centre of diversity in Mexico, with 65 species and endemism above 60% (Alvarado-Cárdenas et al. 2020).During a revision of Matelea for the country, four new species were discovered and are described here.These species are part of the M. gonoloboides (B.L.Rob.& Greenm.)Woodson species complex (Figs 1 and 2), which includes M. medusae Woodson, and M. porphyrantha (Standl.)Woodson (Stevens 2009).This species complex shares rotated corollas, arachnoid trichomes of the adaxial corolla, a cyathiform corona adnate to the base of the column, a distal edge of the corona with five interstaminal bifid and filiform (hornlike) lobes, and five oblong-spatulate staminal corona lobes resting on the anthers.
Specimens associated with the proposed new species have until now been erroneously identified as M. gonoloboides, however, these specimens differ in the shape and components of the gynostegial corona, as well as in their geographic distributions.Thus, we were unable to confidently assign them to any of the named species of the M. gonoloboides complex and have, therefore, described and illustrated them here, as four new species of Matelea for Mexico.We propose conservation status assessments, provide a distribution map of the new species and include a dichotomous key to the species complex.We have also provided a lectotypification of M. gonoloboides s.s.
QGIS software (QGIS Development Team 2019) was used to generate distribution maps based on the geographic and ecological information gathered from the consulted herbaria and the protologues of the previously published species.We complemented the distribution information for Matelea gonoloboides, M. medusae and M. porphyrantha with data from GBIF (GBIF 2019) and Naturalista (Naturalista 2019), see Appendix 1. Duplicate records or those without geographic coordinates were omitted.Mapping followed the proposed regionalisation of the Neotropics of Morrone (2014a, b) and used outlines of the Neotropical regions (Löwenberg-Neto 2014) as background.

Matelea jaimesiae
RECOGNITION.Matelea jaimesiae is morphologically close to M. balrog, but differs in having narrowly ovate blades 1.2 -2.7 cm wide (vs ovate 2.6 -4.2 cm); sepals 2.5 -3.7 × 0.8 -1.3 mm (vs 2.1 -2.5 × 0.7 -0.8 mm); corolla with reticulation (vs not reticulate), corolla lobes (6.4 -) 7 -8.4 mm long, triangular (vs 8.6 -9.6 mm long, lanceolate); gynostegial corona 0.8 -0.9 mm long (vs 0.4 -0.6 mm); Cs with narrowly oblong lobes, with apex spatulate (vs oblong lobes, with apex rounded); base of the Ci lobes with warty membranes with protuberances (vs smooth membranes), lobes of the Ci 1. 3 -1.5 mm long (vs 1.7 -1.8  HABITAT.Matelea jamesiae occurs in the pine-oak forest, oak forest and disturbed areas derived from these types of vegetation, at altitudes of between 1900 -2140 m.CONSERVATION STATUS.Recorded as scarce in the sites where it has been collected, it is known only to the S and SE of the Nevado de Toluca volcano.The EOO is 18,689 km 2 (CR), and the AOO is 12 km 2 (EN).The populations seem to tolerate disturbance, but since they have a very restricted distribution, we propose to assign this species to the category: Endangered (EN B2a, b iv) (IUCN 2022).PHENOLOGY.Collected with flowers from June to August and with fruit in September.ETYMOLOGY.The specific epithet honours Verónica Juárez Jaimes of the National Herbarium of Mexico (MEXU) who is a specialist in the Asclepiadoideae subfamily in Mexico, particularly of the genus Marsdenia R.Br.(now Ruehssia H.Karst.).Mrs Jaimes found and collected specimens of this species for the first time.NOTES.The specimens of Matelea jaimesiae (Figs 1G, H, 2C, D) have previously been identified as M. gonoloboides (Figs 1E, F, 2A, B), but it is distinguished by having a corolla with triangular lobes (vs ovate lobes); Cs with oblong lobes, apex spatulate (vs oblong lobes, apex rounded); Ci with ligulate, erect, curved lobes, 1.3 -1.5 mm long (vs linear, erect, twisted lobes, 2.6 -3.1 mm), free at the base (vs joined), base of the lobes with a warty membrane with protuberances (vs dome crested in the axil of each lobe).The new species occurs in the state of Mexico in the Transmexican Volcanic Belt biogeographic province (vs Oaxaca state, in the Sierra Madre del Sur province) (Map 1).http:// www.ipni.org// urn: Idis: ipni.org: names: 77324 869-1

Discussion
Matelea has morphologically diverse corollas and gynostegial coronas and the group is a continuous source of species-level novelties (Cortez et al. 2018;Juárez-Jaimes et al. 2021;Lozada-Pérez & Alvarado-Cárdenas 2016).Our findings corroborate the recognition that Matelea has a high level of diversity in Mexico, with 69 species and it is the second most diverse group of Apocynaceae in the country, after Asclepias with 72 species (Alvarado-Cárdenas et al. 2020).Likewise, the genus shows a high degree of endemism in Mexico, with 46 species (66.6%) restricted to the country.
The species proposed here are tentatively assigned to the genus Matelea.The phylogenetic relationships in Matelea remain inconclusive until further taxonomic sampling and more robust genetic data provide taxonomic stability (McDonnell et al. 2018).Species of the M. gonoloboides complex have a sister relationship with the genera Dictyanthus Decne.and Polystemma (Krings et al. 2008;McDonnell et al. 2018) but cannot be placed within those genera because Polystemma has a campanulate corolla, usually glabrous, complex and usually in two series; and the whole plant has glandular trichomes with crystalline white inclusions (Stevens 2009).By comparison, species of the M. gonoloboides complex have rotate corollas with arachnoid trichomes, the corona is in one series and, although they share filamentous appendages (Figs 1 and 2) with Polystemma, these arise from the interstaminal region and not the staminal portion.The M. gonoloboides complex also lacks trichomes with crystalline white inclusions.In Dictyanthus, the corona has undivided lobes fused to the corolla and the corolla is campanulate-sacciform (Stevens 2009;Endress et al. 2018) compared to the M. gonoloboides complex in which species have a divided corona and lack the rotate corolla.In addition, M. gonoloboides has been recovered as a sister taxon to Dictyanthus but not to Polystemma (Krings et al. 2008;McDonnell et al. 2018;Keller & Liede-Schumann 2020).Based on these characteristics, the species described here should most probably be circumscribed within Matelea.
The new species described here are an important contribution to our knowledge of Mexican Gonolobinae and of its Matelea species, since they went unnoticed or were incorrectly identified for such a long time.The specimens examined (Figs 1A -D, G -K; 2C -G) were mistakenly identified as belonging to published species of the Matelea gonoloboides species complex because of apparent similarities in floral morphology and a lack of detailed analyses of their morphology (Standley & Williams 1969;Stevens 2009).Taxonomic descriptions made previously in this group did not detail coronal attributes, such as fusion of the Ci lobes, nor the arrangements of any appendages or membranes that were present: these characteristics are taxonomically important and are cohesive for each defined group of specimens studied.Likewise, the geographical distributions of the proposed species (Map 1) show disparities: the species occupy different biogeographic provinces which further helps to delineate and identify them.
A future integration of these new taxa into a phylogenetic analysis may enable us to hypothesise ancestry-descent relationships between the members of the Matelea gonoloboides complex.It would also allow us to contrast their phylogenetic relationships with other clades or taxa recovered previously which are phylogenetically close to M. gonoloboides, such as species of Dictyanthus and other Matelea species (McDonnell et al. 2018).
Identification key to the Matelea gonoloboides species complex

HABITAT. 1 .
Grows on open grassy slopes with clumps of shrubs and trees derived from evergreen and subdeciduous forests, at 1650 -1950 m elevation.CONSERVATION STATUS.Matelea cornuta is known only from two locations in the south of the Sierra Madre of Chiapas (Map 1).There is no population abundance data, but it may constitute a rare species.The EOO cannot be calculated, due to lack of specimens, and the known AOO is 8 km 2 (CR).As a result of the insufficiency of specimens and information, we propose assigning this species to the threat category: Data Deficient (DD) (IUCN 2022).PHENOLOGY.Collected with flowers in August and September.ETYMOLOGY.The specific epithet is given because the interstaminal corona resembles the horns of a bovid.NOTES.Matelea cornuta differs from other species of the genus by having Ci with 5 laminar lobes patent and distally bifid with ascendant projections (Fig.1C, D).This species is like M. gonoloboides (Figs 1E, F, 2A, B), both have Ci lobes fused at the base, but the Map Geographic distribution of the Matelea gonoloboides species complex including the new species.lobes of M. cornuta differ in shape and orientation, they are flattened laterally with two erect projections (vs dorsoventrally flattened with two erect, twisted projections).The new species occurs in Chiapas state, Mexico, in the Chiapas Highlands and Pacific Lowlands biogeographic provinces (vs Oaxaca state, Mexico, in the Sierra Madre del Sur province) (Map 1).
Endemic to Mexico.Known only from the south of the state of Mexico, in the Transmexican Volcanic Belt province.Map 1. Mexico State: Mun.Coatepec Harinas, carretera San Luis, 17 June 2011, F. D. Dorantes-Hernández et al. 231 (MEXU); Mun.San Simón de Guerrero, ranchería Cucha alrededores del Campo Santo, 1 Aug. 1997, T. Prinzie et al. 206 (MEXU); cerca de la ranchería de Cucha, rancho de Olivia Jaimes, 20 July 1996, V. Juárez J. & M. Ortiz O. 658 (MEXU); cerca del arroyo "La Peña", 20 July 1996, V. Juárez J. & M. Ortiz O. 659 (MEXU); Ranchería Cucha sobre la ladera S del terreno campo santo, 17 Aug.2019, C. A. González-Martínez et al. 2001 (MEXU); 2 km al SW de San Simón de Guerrero, Ranchería Cucha sobre la ladera S del terrero del Campo Santo, 28 Sept. 2019, V. Juárez J. et al. 1162, 1162-A (MEXU) mm).DISTRIBUTION.SPECIMENS EXAMINED.MEXICO: DISTRIBUTION.Matelea lokii is endemic to Mexico.It is known only from central and southern Chiapas in the Chiapas Highlands and Pacific Lowlands biogeographic provinces.Map 1. Matelea lokii grows in pine-oak forest and oak forest, between 1140 -2020 m.CONSERVATION STATUS.Matelea lokii is only known from three locations in Chiapas state: La Sepultura Biosphere Reserve, near El Triunfo Biosphere Reserve and in the municipality of Oxchuc in the northeast (Map 1).Known populations are few.The EOO (IUCN 2022) is 4,551,248 km 2 (EN), and the AOO is 12 km 2 (EN).Due to the insufficiency of collections and restricted distribution, we propose assigning this species to the threat category: Data Deficient (DD).PHENOLOGY.Collected with flowers from July to August.ETYMOLOGY.The specific epithet refers to the interstaminal corona that resembles the horns of the helmet used in the fictional representation in the Marvel Cinematic Universe, created by Stan Lee, of the mythical character Loki.NOTES.The specimens of Matelea lokii (Figs 1J, K, 2F, G) had been identified as M. gonoloboides (Figs HABITAT.