Taxonomic revision of South American species of the genus Acacia subgenus Acacia (Fabaceae : Mimosoideae)

Detailed descriptions, habitat preferences, geographic range, and represent ative specimens are given for the 13 native and two introduced taxa of Acac ia subgenus Acacia (approximately the same as Acacia series Gummiferae) tha t are found in the South American flora. Some of these taxa are wide rangin g. Acacia macracantha, A. tortuosa, and A. farnesiana are extremely common in northern South America, whereas A. caven and A. aroma occur throughout m uch of the southern half of the continent. The remaining species have restr icted ranges, being found in relatively small areas. Principal components a nalysis (PCA) of vegetative and floral features shows that these species fo rm discrete groups in plots of the first three principal components. From t hese data, most of the species were found to be relatively homogeneous, as indicated by the tight clusters formed in the PCA plots. In contrast, A. ma cracantha, a species ranging from Florida, south through the Caribbean, int o South America, and in Mexico, is highly variable morphologically. The dat a suggest little gene flow between species. Hybrids are extremely uncommon.