genus Mesoamerantha

Taxonomic Change:

• A genus of Hechtioideae closely related to Hechtia but diagnosable by means of the following character combination: central inflorescence, sessile flowers with a ¾ inferior ovary, and white, rarely apically red petals. It is also restricted to the extreme south of Megamexico.
  
  Etymology and distribution: Mesoamerantha alludes to fact that this new genus is restricted to the Mesoamerica region, particularly to Nicaragua, El Salvador, Honduras, Guatemala, and Belize, in pine-forest or low caducifolious forests.
  
  Three species are recognized in this genus and are distributed in the biogeographical provinces of Chiapas Highlands, Pacific Lowlands, Mosquito, and Veracruzan (sensu Morrone, 2014). —See Ramirez et al. 2018b p. 308

Comments:

• Mesoamerantha I. Ramírez & K. Romero is a monophyletic group in Bromeliaceae subfam. Hechtioideae Givnish recently segregated from Hechtia Klotzsch, based on the results of a phylogenetic analysis derived from the evaluation of molecular, morphological, and geographical evidence (Ramírez-Morillo et al., 2018a, 2018b; Fig. 1). In its current circumscription, this genus contains three species, distributed in the southernmost part of Megamexico III (Rzedowski, 1991), within the political limits of Belize, El Salvador, Guatemala, Honduras, and Nicaragua. Species of Mesoamerantha are an ecologically important component of the lithophytic and terrestrial flora in the tropical deciduous and pine-oak forests of northern Central America.
  
  Mesoamerantha species share many characters with the rest of the species in Hechtioideae, especially their terrestrial or lithophytic habit, caespitose, succulent rosettes of spiny leaves, and dioecious sexuality, with unisexual, diurnal, fragrant flowers. A phylogenetic analysis based on molecular (plastid and nuclear DNA) and morphological evidence supports the monophyly of the genus (Ramírez-Morillo et al., 2018a; Fig. 1). The only morphological synapomorphies of Mesoamerantha, to the extent of our study, are the presence of a three-quarters inferior ovary, and thus, of fruits that are formed by the ovary walls and the basal portions of the petals and sepals and that do not retain the free portions of the sepals, petals, and stigmatic lobes, as in species of Bakerantha L. B. Sm. and Hechtia with superior ovaries. Wholly or partially inferior ovaries have evolved at least twice in the subfamily: in a clade formed by H. deceptrix I. Ramírez & C. T. Hornung and H. epigyna Harms, and in Mesoamerantha. Nevertheless, additional characters facilitate the identification of the genus and its species: a central inflorescence (featuring the strict monocarpic growth pattern sensu Ramírez-Morillo et al., 2014), as well as a geographical range restricted to the region from Guatemala extending to the central-northern, mountainous region of Nicaragua, with a disjunct population in Belize (M. guatemalensis (Mez) I. Ramírez & K. Romero in Cayo District). Only three species are included in this genus: M. dichroantha (Donn. Sm.) I. Ramírez & K. Romero, M. guatemalensis, and M. malvernii (Gilmartin) I. Ramírez & K. Romero (Ramírez-Morillo et al., 2018b).
  
  Smith and Downs (1974) grouped the three species of Mesoamerantha (as Hechtia) with H. epigyna, a species native to Mexico (state of Tamaulipas), because they share a partially or completely inferior ovary, diagnosing H. epigyna on the basis of its pedicellate flowers with pink petals. The phylogenetic hypothesis of Ramírez-Morillo et al. (2018a) placed H. epigyna nested within Hechtia s. str. and sister to H. deceptrix, both endemic to the Sierra Madre Oriental biogeographical province in Mexico. While those two species share a wholly inferior ovary, Mesoamerantha species show a three-quarters inferior ovary.
  Mesoamerantha guatemalensis, the type species of Mesoamerantha, was first named as Hechtia guatemalensis Mez based on a collection from Guatemala (department of Guatemala) (Mez, 1906). The type specimens (H. Pittier 137; holotype, US!; isotypes, B!, GH!) consist of a leaf and fragments of a staminate inflorescence. This species has long been considered the most widely distributed, ranging from Belize to Nicaragua. Furthermore, some authors have considered this species to feature great morphological variability (Burt-Utley & Utley, 1994; Utley & Burt-Utley, 2001) and to be potentially confusable with M. malvernii, which was first described as H. malvernii Gilmartin from the locality of El Paraíso in Honduras. Type specimens (A. J. Gilmartin 966; holotype, US!; isotypes, EAP!, US!) consist of a single leaf and fragments of an inflorescence with immature capsules. It has been found to be endemic to Honduras (Gilmartin, 1965; Smith & Downs, 1974; Burt-Utley & Utley, 1994; Utley & Burt-Utley, 2001; Nelson, 2008). Because both species have been described from individuals with different sexual structures (staminate or pistillate), a comparison of their types is less than informative because most species in Hechtioideae show sexual dimorphism (Ramírez-Morillo et al., 2018b).
  Mesoamerantha dichroantha was described as Hechtia dichroantha Donn. Sm. by Smith (1906) from Guatemala (department of Baja Verapaz). Type specimens (O. F. Cook s.n.; holotype, US!; isotypes, GH!, US!) consist of a leaf and fragments of a staminate inflorescence. The species was later reported as occurring in Honduras (i.e., Smith, 1958; Molina, 1975; Utley & Burt-Utley, 2001; Nelson, 2008) and Mexico (Gilmartin, 1965); however, these reports are not verified, as vouchers were not cited in these publications, and no specimens belonging to this species were found during extensive searches in herbaria and field trips. Specimens collected in Honduras (departments of El Paraíso and [Francisco] Morazán), referred to M. dichroantha by Gilmartin (1965), Smith and Downs (1974), and Burt-Utley and Utley (1994), were examined by us and are best referable to M. malvernii, as circumscribed here and discussed below. Thus, M. dichroantha appears restricted to Guatemala.
  
  In this contribution, we propose epitypes for both Mesoamerantha dichroantha and M. malvernii, two taxa that exemplify the problems associated with Hechtioideae taxonomy (Ramírez-Morillo et al., 2012). Hechtioideae species are dioecious and the flowers are ephemeral whereas the capsules are long lasting. Consequently, descriptions of many taxa have been more often based upon fruiting material and less often on flowering (either staminate or pistillate) specimens. As explained above, M. malvernii was based upon material with immature fruits, and both the protologue and subsequent taxonomic treatments of the species (e.g., Flora Mesoamericana [Burt-Utley & Utley, 1994], Flora Neotropica [Smith & Downs, 1974], and Flora de Nicaragua [Utley & Burt-Utley, 2001]) lack information on the staminate structures. On the other hand, M. dichroantha was based on a specimen bearing a staminate inflorescence. Because of the lack of information on the morphology of both sexes for the two species and the general similarity of their rosettes, staminate specimens of M. malvernii have been mistakenly identified as M. dichroantha. Examples of this confusing situation are evident in some taxonomic treatments of M. dichroantha (e.g., Gilmartin, 1965), where descriptions of what supposedly are its pistillate flowers (e.g., Gilmartin 948, US) correspond to M. malvernii. The collections referred to M. dichroantha in Flora Mesoamericana (Burt-Utley & Utley, 1994) are also confusing. These include Molina 25975 (EAP, F, G, MO, NY, US), best identified as a staminate inflorescence of M. malvernii, whereas King & Diboll 3282 (MICH), most likely a duplicate of King 3282 (TEX, US), from Salamá, Baja Verapaz, Guatemala (5 km in a straight line from the type locality of M. dichroantha), is a pistillate individual of the latter species. Thus, the circumscriptions of both species are incomplete and confusing. In order to prevent future misidentifications of both taxa, epitypes for the two names are here designated, as well as complete morphological descriptions, distributional discussions, habitat notes, illustrations, and assessments of conservation status using the IUCN methodology, for all species in Mesoamerantha, based on all available herbarium specimens. An artificial key is also included to identify live as well as herbarium specimens for all taxa. —See Romero et al. 2022