Abstract:

The genus Prosopidastrum (Mimosaceae) was described by Burkart on the basis of two species: P. mexicanum (Dressler) Burkart from Mexico with fruits 12 mm wide, dehiscing by two valves dividing into 1-seeded segments, these separating from a persistent replum, with leaflets 4-8 × 2-4 mm, and P. globosum (Gillies ex Hooker f. & Arnott) Burkart from Argentina, which has loments 3-4 mm wide and leaflets 0.5-2 × 0.5-1 mm. Burkart noted the Argentinean P. globosum as polymorphic. Based on fieldwork, analysis of herbarium specimens, and palynological studies, we concluded that three entities new to science must be described: P. dehiscens, P angusticarpum, and P. gracile. The new species are restricted to Argentina and are mostly allopatric, but rarely locally sympatric. Characters of fruit, flowers, pollen, and leaves identify each new species. A key to differentiate all the known species is provided, as well as a key to identify the Argentinean species based on pollen morphology.