Morphometric Investigation of a Species Complex in Section Series (Leguminosae, Caesalpinioideae).

series was created by Barneby in 1991, embracing species diagnosed by their small subshrubby habit and the presence of gland-tipped setae and trimerous flowers. Most species are endemic to Northeastern Brazil, and some possess characters deemed diagnostic which nonetheless overlap, making species identification difficult. Our study aimed to test species circumscriptions and sets of characters that could be applied to unequivocally distinguish the species. Twelve populations (225 individuals) were collected at nine localities, encompassing the Brazilian vegetation types , and . Linear measurements of 38 floral and vegetative characters were measured and analyzed using Canonical Variate Analysis and cluster analysis. The first two canonical axes explained 41.4% and 18.9% of the variation and separated two populations of the group recently described as a new species. Vegetative characters are more informative for species delimitation than flower characters, and most groups are distinguished primarily by the number of pinnae pairs, number of leaflets per pinna and length of the leaf rachis. The species displaying the highest morphological similarity are , and . The traditional morphometric approach was capable of objectively dealing with a type of variation that would be difficult to interpret by purely examining herbarium specimens.