Pilocosta, a New Genus of Tropical American Melastomataceae

Abstract

Pilocosta, here proposed as a new genus of Tibouchineae, is distinguished by its solitary axillary, ebracteate flowers, 4-merous floral pattern, and quadrangular, prominently ribbed hypanthia. Delimitation of taxa, based on gross morphology and chromosome numbers, is tempered by field observations of variation in natural populations. Data from these sources provide a rationale for recognizing three species-P. erythrophylla, P. nana, and P. oerstedii. The latter comprises subsp. oerstedii and the newly described subsp. campanensis. Counts of n = 7 and 14 for P. erythrophylla, n = 33 for P. nana, and n = 18 for P. oerstedii subsp. oerstedii are reported for the first time. A systematic treatment is presented for the four recognized taxa, with a key, synonymies, typifications, descriptions, discussions, and diagnostic illustrations for representative taxa.