Lachemilla mexiquense (Rosaceae), a new species from Mexico

Abstract A new species of Lachemilla (Rosaceae), Lachemilla mexiquense D.F. Morales-B., from Mexico is described and illustrated. This species is similar to Lachemilla aphanoides by its tripartite leaves and glomerulate inflorescence with entirely glabrous flowers, but it differs by its stonoliferous habit, persistent basal leaves and basal stipules, and smaller flowers with a campanulate-elongate hypanthium and single carpel. A key to the species of Lachemilla in Mexico is provided.


Introduction
Lachemilla Focke (Rydb.) is a morphologically highly variable group that includes perennial herbs, sub-shrubs, and shrubs. It comprises ca. 80 species and occurs between 2200 and 5000 m in elevation in the high mountains of the Neotropics, from northern Mexico to northern Argentina and Chile (Romoleroux 1996;Gaviria 1997), where it is one of the main elements of the páramo and superpáramo fl ora in South America. In Mexico the genus is represented by at least 10 species that can be found in sub-alpine and alpine habitats from the mountain pine forest to the high elevation zacotanales. Lachemilla has a nearly ubiquitous occurrence throughout the montane American tropics and remains a taxonomically complex group where species boundaries are often unclear and the infrageneric taxonomy is poorly defi ned. Since the only comprehensive revision of Lachemilla (Perry 1929), several works have tried to clarify its taxonomy (Rothmaler 1935(Rothmaler , 1937Notov and Kusnetzova 2004) and recently several regional treatments have been published (Romoleroux 2004;Barrie 2015), but a complete revision of the group is still needed. Recent taxonomic work aiming to produce a monographic treatment of Lachemilla has resulted in the description of several new species (Romoleroux 2009;Romoleroux and Morales-Briones 2012).

Distribution and ecology.
Lachemilla mexiquense is only known from the State of Mexico, municipality of Ocuilan, at ca. 3050 m altitude ( Figures 2B, 3). Lachemilla mexiquense grows at the border of dense forest of various species of Pinus. Th is species lives in sympatry with Lachemilla procumbens (Rose) Rydb., L. vulcanica (Schltdl. & Cham.) Rydb., and L. aphanoides (Mutis ex L. f.) Rothm. It was collected in fl ower and fruit in late June.
Etymology. Th e specifi c epithet refers to the demonym for State of Mexico where the type specimen was collected.
Conservation status. Lachemilla mexiquense has a very limited geographic distribution, and is only known from the type locality ( Figures 2B, 3). It occurs right outside the limits of the Cumbres del Ajusco National Park and Lagunas de Zempoala National Park. Th e type locality has been severely impacted by human activities, including conversion to agriculture (sheep and cow grazing). Following the IUCN (2014) guidelines, based on the reduced geographic distribution and altered land use at the type locality, this species should be categorized as endangered (EN), at least until other populations are discovered.
Notes. Lachemilla mexiquense resembles L. aphanoides by having tripartite leaves with bifi d lateral segments and glomerulate infl orescence with entirely glabrous fl owers. Nevertheless, L. mexiquense diff ers from L. aphanoides by its caespitose habit, creeping stems, and stolons that form dense mats. Also, the basal leaves and basal stipules are persistent, and fl owers are smaller (1.2-1.5 mm long) with a campanulateelongate hypanthium and single carpel. Lachemilla rupestris (Kunth) Rothm., a species from Andean South America with similar habit, diff ers from L. mexiquense by having entire lateral segments of the leaves, yellow-brown membranaceuos basal stipules, and larger fl owers (2.5-3 mm long) with a turbinate-campanulate hypanthium, sericeoushirsute pubescence, and 2-4 carpels.
In addition, phylogenetic analyses of chloroplast and nuclear DNA (Morales-Briones et al. unpubl. data) clearly separate L. mexiquense from L. aphanoides and L. rupestris. Th e chloroplast phylogeny place it as sister species of the 'Orbiculate group,' which encompasses species with stoloniferous habit, palmately lobed or cleft leaves, and fl owers disposed in profuse terminal cymes, like Lachemilla pectinata (Kunth) Rothm. Th e nuclear phylogeny fails to confi dently resolve the phylogenetic position of L. mexiquense, suggesting that it may be of hybrid origin, a common pattern seen throughout Lachemilla.

Key to the species of Lachemilla in Mexico
Notes. Adapted from Standley and Steyermark (1946), Romoleroux (2004), and Barrie (2015). Accepted taxa and synonymy follows the regional revisions of Romoleroux (2004) and Barrie (2015), with the exception of L. sibbaldiifolia (Kunth) Rydb. and L. pringlei Rydb., which based on extensive fi eld observations and the examination of herbarium material, are considered here as two distinct taxa.