Taxonomic studies on the genus Indigofera Linn. (Indigofereae, Fabaceae) in parts of Katsina and Kaduna States, North-Western Nigeria

Indigofera is a large genus in the family Fabaceae comprising about 750 species. In Nigeria, particularly the northwestern savanna region, identification and naming of Indigofera species have been very difficult, ambiguous and controversial for a long time. Thus, proper identification and naming of the species within this genus are paramount. Several field surveys were carried out in the study area and twelve species were successfully collected and identified. Multivariate analyses (CA and PCA) were used to determine whether the species are distinct or not, and to identify the most useful characters for the identification of the species in the region. Fresh specimens were collected purposely for this work and herbarium specimens were used. The result of the cluster analysis revealed 12 distinct clusters (at an Euclidean distance of 0.08) with a cophenetic correlation coefficient value (r) of 0.89. The result of the PCA revealed 12 distinct groups. The character loadings indicated that number of seeds per pod, petiole length, leaflet length, internode, fruit length and leaflet width contributed the highest variation among the species, which could be more useful in delimiting the species. These characters can, therefore, be used in the identification and distinguishing of Indigofera species in the region. We provided a key for the identification of the species.