Chusquea septentrionalis sp. nov. (Poaceae: Bambusoideae) from the Madrean region in Durango, Mexico

Chusquea is a monophyletic genus divided into five subgenera. Chusquea subg. Swallenochloa is recognized based on the combination of a more or less shrubby and clumping habit, often relatively short internodes, and the usual presence of intravaginal branching. It is distributed from Mexico to Chile, with species also in the mountains of eastern and southeastern Brazil, commonly occupying high elevation grasslands, although a few species inhabit montane forests. Based on the review of herbarium specimens and fieldtrips to the Sierra Madre Occidental in the state of Durango, Mexico, we here describe and illustrate Chusquea septentrionalis, the newest species to be classified within subgen. Swallenochloa. This novelty is compared with the rare, high elevation Mexican endemics C. matlatzinca and C. perotensis, from which it can be separated by its thick-walled, hollow culms, intravaginal branching pattern, central bud slightly larger than the subsidiary buds, subsidiary buds axillary and arranged linearly, and the long inner ligule of the foliage leaves. Chusquea septentrionalis is referred to Chusquea subgen. Swallenochloa sect. Swallenochloa, because of the morphological characters that it shares with the rest of the species in this section, especially the branching pattern. With the description of this new species, the diversity of native Chusquea and woody bamboos overall in Mexico increases to 22 and 52 species, respectively. Due to the reduced distribution of this new species, we propose to include it in the Norma Oficial Mexicana (NOM-059-SEMARNAT-2010) and IUCN red list for its protection. A morphological key to the species of C. sect. Swallenochloa known from Mexico is provided.