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Introduction
The main mountain chains of Mexico, including the Transmexican Volcanic Belt (TMVB), form the Mexican Transition Zone (MTZ) (Morrone, 2020). Within the MTZ, orogeny, volcanism and paleoclimatic changes have promoted biological speciation and local survival (Mastretta-Yanes et al., 2015). As a result, angiosperm species richness is concentrated there (Cruz-Cárdenas et al., 2013; Rodríguez et al., 2018; Sosa et al., 2018; Mishler et al., 2020). The Mexican angiosperm flora totals 22,126 species (Villaseñor, 2016), although Joppa et al. (2011) estimated that 15% remains to be discovered and Espejo Serna (2012) calculated that this percentage is around 30.8%.
The genus Echeandia Ortega (Asparagaceae) characterizes the Mexican geophyte flora (Rzedowski, 2019). It has 85 species, 74 of which grow in Mexico and 63 are endemic to this country (Espejo Serna, 2012; Ortiz-Brunel et al., 2021). The genus ranges from the southwestern United States of America to southern Peru, but several species have narrow geographic ranges. The number of species is increasing since more areas are being explored and detailed analyses are made based on herbarium specimens (Cruden, 1999; López-Ferrari et al., 2002; Rodríguez and Ortiz-Catedral, 2013; Rodríguez and Ortiz-Brunel, 2019). Both field and herbarium work led us to name and describe a new species, which are the objectives of this study.
Materials and Methods
During a systematic study of Echeandia, we collected tall plants of this genus within the boundaries of the Cholula archaeological site, Puebla. Later, we discovered another population in Tlaxcala. Finally, we found two herbarium specimens (Boege 1478) deposited at the National Herbarium of the Universidad Nacional Autónoma de México (MEXU). These were collected at the Xochitécatl archaeological site in the state of Tlaxcala. All populations were from sites in the Transmexican Volcanic Belt. After the analysis of the vegetative and floral characters of these plants, we concluded that they represented an undescribed species. The morphological description and illustration were based on eight voucher specimens plus living plants from two populations. We followed the terminology described by Moreno (1984). Moreover, we assessed its conservation status by calculating its extent of occurrence (EOO) and its area of occupancy (AOO) using the GeoCAT tool (Bachman et al., 2011) and based on the IUCN Red List Categories and Criteria (IUCN, 2019).
Results
Taxonomy
Echeandia cholulensis Aarón Rodr. & Ortiz-Brunel, sp. nov., Figs. 1-2.
Figure 1: Echeandia cholulensis Aarón Rodr. & Ortiz-Brunel. A. habit; B. inflorescence detail; C. flower; D. tepals; E. androecium, gynoecium; F. capsule, seeds. Drawn by Juvenal Aragón Parada from the type (A. Rodríguez and L. Ortiz-Catedral 2987).
Figure 2: Photos of Echeandia cholulensis Aarón Rodr. & Ortiz-Brunel and its morphologically related species. A. inflorescence; B. fruits; C. inflorescence of E. robusta Cruden; D. inflorescence of E. michoacensis (Poelln.) Cruden. Photos by Aarón Rodríguez.
TYPE: MEXICO. Puebla, municipio San Andrés Cholula, pirámide de Cholula, 2187 m, 19°03'27.8''N, 98°18'5.27''W, 08.VII.2002, A. Rodríguez and L. Ortiz-Catedral 2987 (holotype: IBUG!, isotype: MEXU!).
Plantae robustae; radicum parte incrassata ab cormo 3-4 cm distante; foliis basalibus 6-9, lanceolatis, undulatis, 50-60 cm longis, 4-5 cm latis, marginibus hyalinis; scapo glabro, 1-1.6 m alto, subtento in dimidio inferiore per bracteam longifoliaceam, ramo 0-1; scapi bracteis 6-8, ab basin vaginantes; tepalis albis, reflexus; tepalis externis ellipticis, 15-17 mm longis, 4-5 mm latis; tepalis internis ellipticis, 15-17 mm longis, 5-7 mm latis; filamentis cylindricis vel clavatis, muricatis, 8 mm longis; antheris liberis, sagittatis, dorsifixis, 6 mm longis, lateraliter dehiscentibus; stylo 13 mm longo; ovario cylindrico, 4 mm longo, 1.5 mm lato; capsula elliptica, 9-11 mm longa, 4-5 mm lata.
Perennial herbs, 100-160 cm high, including the inflorescence; root-thickenings 3-4 cm from the corm, 2-4 cm long; basal leaves 6-9, lanceolate, glaucous, margin hyaline, entire, undulate, 50-60 cm long, 4-5 cm wide; inflorescence racemose, rarely 1-branched; peduncle glabrous, ca. 100 cm long, bracts 6-8, the lower half of the peduncle enveloped by long-sheathing leafy bracts; raceme ca. 60 cm long; flowers pedicellate, ascendant, opening in the morning; pedicels green, 10-15 mm long, articulated at the middle; tepals white, reflexed, with 5 green longitudinal nerves; outer tepals elliptic, 15-17 mm long, 4-5 mm wide, acute; inner tepals elliptic, 15-17 mm long, 5-7 mm wide, acute; filaments white, linear, cylindric to clavate, muricate, ca. 8 mm long; anthers sagittate, dorsifixed, free, ca. 6 mm long, dehiscing through longitudinal slits; style white, ca. 13 mm long, surpassing the anthers by ca. 3 mm; stigma capitate; ovary green, narrowly oblong to narrowly ellipsoid, 3-4 mm long, ca. 1.5 mm diameter; capsule green, ellipsoid, 9-11 mm long, 4-5 mm wide; seeds deltoid, folded, black, opaque, 1-1.5 mm long, 1-1.5 mm wide.
Etymology: the specific epithet refers to the Cholula archeological site.
Distribution and ecology: Echeandia cholulensis is known from three collections in the states of Puebla and Tlaxcala (Fig. 3). It has been collected in the valleys around the cities of Puebla and Tlaxcala. It grows in open areas with heavy clay soils and gullies with secondary vegetation derived from the pine-oak forest. It has been found between 2200-2400 m elevation. The populations have numerous individuals. The flowers open during the morning and remain so until early afternoon.
Figure 3: Distribution of Echeandia cholulensis Aarón Rodr. & Ortiz-Brunel, E. michoacensis (Poelln.) Cruden, and E. robusta Cruden in Mexico.
Phenology: the flowering and fruiting period extends from July to October.
Conservation status: EOO and AOO values were estimated at 42.705 km2 and 12 km2, respectively. Based on the criteria B1a and B2a, established by the IUCN (2019), the new species should be considered as Endangered (EN). Its geographical range lies within the urban areas of Puebla and Tlaxcala. This area is under severe pressure due to the agricultural practices and urban growth. According to the RBG Kew (2016) assessment, both processes represent the first and third causes of plant extinction, respectively. However, Echeandia cholulensis was collected within the boundaries of two archaeological sites: Cholula and Xochitécatl. In Cholula, the population has numerous individuals. As a consequence, both populations are safeguarded since Mexican archaeological sites are protected by federal law.
Additional specimens examined: MEXICO. Tlaxcala, municipio Tepetitla de la Solidaridad, Xochitécatl, 2368 m, 19°14'44.61''N, 98°21'0.17''W, 11.X.1970, L. W. Boege 1478 (MEXU); cerca de La Corona, 2.3 km antes de llegar a la caseta de cobro, 2286 m, 19°19'5.41''N, 98°24'27.56''W, 09.IX.2018, G. Munguía-Lino et al. 567 (IBUG, IEB, MEXU, UAMIZ).
Discussion
Morphologically, Echeandia cholulensis resembles E. michoacensis (Poelln.) Cruden and E. robusta Cruden (Fig. 2). All three species include robust plants with root-thickenings distant from the corm, muricate filaments, and free ascending anthers. Echeandia cholulensis and E. robusta have white tepals, while those of E. michoacensis are yellow (Cruden, 1987; 1993). The inflorescence of E. cholulensis is unbranched or produces only one basal branch, in contrast to that of E. robusta which branches several times. The flowers of E. cholulensis open during the morning and the anthers dehisce by longitudinal slits. Conversely, in E. robusta the anthesis occurs in the afternoon with the release of pollen by apical pores. Echeandia cholulensis occurs in the pine-oak forest or secondary vegetation derived from it, above 2000 m elevation and along the TMVB in Puebla and Tlaxcala. Collections of E. robusta have been made in southern Jalisco, along the Pacific slopes of the Sierra Madre del Sur. It grows in savannah-like vegetation (Rzedowski and McVaugh, 1966; Rzedowski, 1978), between 500 and 1000 m a.s.l. (Fig. 3).
Cruden (1999) divided Echeandia into subgenera Echeandia and Mscavea Cruden. The former includes plants with flowers opening early in the morning, commonly with elliptic white or yellow tepals, and ellipsoidal fruits. Most species grow above 1500 m elevation. In contrast, plants in the subgenus Mscavea have flowers which open near noon or later, most of them have narrowly elliptical white tepals and globose fruits. These plants grow below 1500 m elevation. According to this, E. cholulensis pertains to E. subg. Echeandia.
Villaseñor (2016) listed 22,126 species of angiosperms for Mexico with 49.8% of them endemic. This number defines Mexico as a hotspot with a diverse flora, ranking it fifth worldwide (RGB Kew, 2016). Based on Sosa et al. (2018), most Mexican plant lineages diversified around 5-20 million years ago, which coincides with the TMVB formation (Ferrari et al., 2012). Consequently, orogeny, volcanism and paleoclimatic changes facilitated the diversification and persistence of the Mexican plant species on the mountainous areas of the country (Mastretta-Yanes et al., 2015; Muellner-Riehl et al., 2019). The diversification of Dioon Lindl. and Quercus L. fits in this scenario (Gutiérrez-Ortega et al., 2018; Hipp et al., 2018).
Yet, several species of plants remain to be discovered, named, and described. At a global scale, Joppa et al. (2011) estimated that this proportion is about 15%, while Espejo-Serna (2012) calculated that this percentage is around 30.8% for the Mexican flora. Herbaria hold millions of plant specimens, but Goodwin et al. (2015) assessed that more than 50% of the tropical collections could be incorrectly identified. Our work highlights the importance of herbaria revision, since botanical exploration provides specimens, but many of these wait inside herbarium cabinets to be reviewed or identified.
