Sommera cusucoana, a new species of Rubiaceae from Honduras

Abstract Sommera cusucoana Lorence, D. Kelly & A. Dietzsch, sp. nov., (Rubiaceae), a new species from Honduras, differs from the other Mesoamerican Sommera species by the combination of large, obovate leaves with long red petioles, glabrous or glabrate intervenal areas, red stipules, lax, sparsely pubescent inflorescences with red axes, flowers with red hypanthium and calyx, long fruiting pedicels, and dark red mature fruits. It is known only from the type locality in Cusuco National Park.


Introduction
Sommera Schltdl. is a genus of Rubiaceae ranging from southwestern Mexico through Central America to South America, usually below 2000 m elevation in evergreen wet forests and riparian forests or less often in drier pine-oak forests (one species). Th e genus comprises about 10 species of shrubs or small trees characterized by relatively large and soon deciduous paired intrapetiolar stipules; relatively large leaves often strigose-pubescent on the veins beneath, with conspicuously parallel, lineolate minor venation; relatively few-fl owered axillary or subaxillary cymes; small externally pubescent fl owers; and fl eshy 2-locular berries with numerous small, angulate seeds. Although traditionally placed in subfamily Cinchonoideae tribe Mussaendeae (e.g. Borhidi 2006, Dwyer 1980, recent molecular studies indicate Sommera belongs in subfamily Ixoroideae, tribe Condamineae (Bremer 2009).
L. O. Williams (1973) reviewed the Central American and Mexican Sommera species but failed to provide a diagnostic key or illustrate his four new species. Lorence (1993) described and illustrated Sommera parva Lorence, a diminutive new species from Chiapas. In his treatment of the genus for Flora Mesoamericana Lorence (2012) recognized six species from the Mesoamerican region (Chiapas and the Yucatán Peninsula to the Panamá/Colombia border). One additional species (S. grandis (Bartl. ex DC.) Standl.) occurs in southwestern to western Mexico outside the Mesoamerican region, and two more have been described from South America (in Colombia, Peru, and Brazil).
During the course of an ecological survey of montane rain forest vegetation in Cusuco National Park in Honduras (Figure 1), a striking new species of Sommera was discovered. Although only a single individual was collected, this new species is immediately distinguished from the other Mexican and Mesoamerican Sommera species by its red petioles, stipules, infl orescences, hypanthia, fruits and infructescences, and long fl owering and fruiting pedicels. Diagnosis. Diff ers from its congeners by the combination of large, obovate leaves with long red petioles, glabrous or glabrate intervenal areas, red stipules, infl orescences 2-4-fl owered, sparsely pubescent, with red axes, fl owers with red hypanthium and calyx, and mature fruits dark red with long pedicels.
Habitat Th e type locality, at 1333 m, is at the bottom of a deep, narrow valley, about 25-50 m from the bank of a small river. Th e site is riparian rain forest, dominated by tall trees, mainly Liquidambar styracifl ua L. and Cedrela odorata L. Th e microclimate is moist and the vegetation lush and species-rich. Th e vicinity shows minor levels of disturbance: human disturbance due to the proximity of a seasonal camp-site with radiating trails, and natural disturbance due to wind-throw, and land-slips on the steeper slopes.
Etymology. Th e name honors the Cusuco National Park in which it was found. Discussion. Sommera cusucoana diff ers from its Mesoamerican congeners by the combination of large, obovate leaves with long red petioles, glabrous or glabrate intervenal areas, red stipules, lax, sparsely pubescent 2-4-fl owered infl orescences with red axes, fl owers with red hypanthium and calyx, and long fl owering and fruiting pedicels. Floral hypanthia and fruits of S. cusucoana are bright red at all developmental stages. Herbarium label notes for other Sommera species indicate fruits are green when immature and ripen red, at least in S. chiapensis, S. donnell-smithii and S. montana, and possibly white in S. grandis (Mexico). Only S. chiapensis Brandegee (Chiapas, Guatemala, Honduras) has fl owers with similarly short, broadly triangular calyx lobes 1-2 mm long, but it diff ers in having shorter petioles 2-5 cm long, cymes with (4-)6-12 fl owers, shorter corollas with tube 4-8 mm long, and smaller fruits 5-9 mm in diameter.
Updated key to the Mesoamerican Sommera species 1 Leaves glabrous beneath or strigillose only on the costa, even when young.

. S. donnell-smithii
Th is is the third species new to science discovered in Cusuco National Park by the Operation Wallacea Forest Botany team, the others being the tree Hondurodendron urceolatum Ulloa et al. (Aptandraceae: new genus and species) (Ulloa Ulloa et al. 2010, Kelly et al. 2011) and the herb Calathea carolineae H. Kenn. (Marantaceae) (Kennedy 2012). Th e type specimens of C. carolineae and S. cusucoana were collected at the same locality.
Sadly, this type locality is within 0.5 km distance of areas of extensive clear-fell, deep within the National Park, that were logged in the period 2010-13. Although the range of Sommera cusucoana has yet to be established, this relatively conspicuous and distinctive species has not been noted elsewhere within the Park, and its proposed conservation status must be Critically Endangered (IUCN 2000(IUCN , 2013.