Systematics of the Nasa poissoniana group (Loasaceae) from Andean South America

The monophyletic Nasa poissoniana group (Loasaceae, subfamily Loasoideae) is revised on the basis of extensive field studies, observations in cultivation and the revision of herbarium specimens. A core of taxa has been considered as closely allied on the basis of morphology in the past, but several additional taxa have been recognized as allied to this group on the basis of molecular data. One species, N. raimondii, formerly placed in the N. stuebeliana group, is now transferred to the N. poissoniana complex as a result of the molecular findings. Nasa poissoniana ssp. glandulifera is described as new to science on the basis of morphologically divergent collections of N. poissoniana from two northern departments of Peru. Numerous new localities, often far from the previously known distribution area, are reported for several species. The N. poissoniana group has its centre of diversity in the inner Andean valleys of southern Peru, quite unlike all other groups of Nasa, with centres of diversity in the Amotape-Huancabamba Zone in northern Peru and southern Ecuador. Descriptions, drawings and a distribution map and key to all taxa are provided, and detailed information on habitat and distribution is given for each species. (C) 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 278-301.