keywords: Delimitation, Millettia species, morphometric, Principal component analysis, qualitative characters
In spite of a century long research on Millettia (Fabaceae-Papilionoideae) species, the taxonomy remains controversial. In attempt to resolve this problem, a detailed morphological study was conducted on some indigenous Nigerian species to elucidate their taxonomic relationships to present complementary data to aid the identification of the species. Morphological characters were assessed for stable, distinctive and diagnostic characters for the delimitation of these species. Qualitative characters were noted and recorded while the quantitative features were measured with a ruler and thread. All the data were recorded and subjected to appropriate statistical analyses. Results from the principal component analyses (PCA) were used to explore variations in the quantitative characters among Millettia species, and cluster analyses were used to ascertain systematic groupings of the taxa. Results from the macro-morphological examinations showed that the leaflet shape varied among species while leaflet types, apex, base, margin and arrangement are similar in all species. Occurrence of stipel, presence or absence of hairs on the leaf surface, pedicel and fruit clearly distinguished the species from one another. In general, other attributes such as leaflet length and width, lamina length, fruit length and width, number of leaflet pairs per leaf and number of lateral nerves of leaflets were species-specific. The similarity in morphology indicates interspecies relationships, which justify their groupings together in the same genus while the differences confirm their delimitation as distinct species. A new identification key has been constructed other than the ones used in the flora of West Tropical Africa.