A SYSTEMATIC STUDY OF DIGITARIA SECT PENNATAE (POACEAE, PANICEAE) IN THE NEW-WORLD

New World Digitaria sect. Pennatae is represented by two species: D. a renicola and D. cognata. Reproductive, cytological, and morphological studies were conducted with four accessions of D. arenicola and 25 acc essions of D. cognata. Based on these studies, D. arenicola and D. cog nata are treated as separate species, the latter with two subspecies. A key to the New World species in sect. Pennatae, with descriptions an d nomenclature is given. All observed mature embryo sacs were not apos porous and were tentatively classified as sexual. They were typical Po lygonum-type megagametophytes. Chromosome numbers were determined from root tip cells. The chromosome number for D. arenicola is 2n = 4x = 3 6, the first record for this taxon. For D. cognata subsp. cognata, 2n = 4x = 36, and for D. cognata subsp. pubiflora counts are primarily 2n = 8x = 72, but 2n = 4x = 36 is occasionally found.