Molecular systematics of Indian Crotalaria (Fabaceae) based on analyses of nuclear ribosomal ITS DNA sequences

Crotalaria L. (Fabaceae) comprises approximately 700 species that are distributed in tropical and subtropical regions of the world. In India, it is the largest legume genus with 92 species. Sequences of the nuclear internal transcribed spacer from species representing all the six recognized sections of Indian Crotalaria were subjected to phylogenetic analyses. Ancestral state reconstructions were done for two morphological characters, corolla keel beak, and leaf form. Analyses reveal five major well-supported clades within a monophyletic Crotalaria. Clade 1 has members with rostrate-spirally twisted keel beaks while the remaining four clades comprise members with keel beaks rostrate-not spirally twisted. Clade 1 further bifurcates into two clades characterized by differences in leaf morphology: (1a) contains species with simple leaves belonging to section Calycinae, section Crotalaria subsection Crotalaria and subsection Bractetae and multifoliolate leaves belonging to section Crotalaria subsection Polyphyllae (1b) contains species with trifoliate leaves belonging to section Dispermae, section Crotalaria subsection Longirostres. Sub-clade iii in Clade 1a contains four species complexes, each forming a monophyletic group. Of these one comprising C. madurensis, C. subperfoliata, C. shevaroyensis, and C. longipes is endemic to a region in southern India. Each of the others contains one endemic species and one widespread species that is sympatric with the endemic one (C. hirta and C.mysorensis; C. epunctata and C. albida; C. clarkei and C. triquetra). The present study suggests that: (1) all members of section Calycinae and most members of section Crotalaria form a clade, (2) members of section Crotalaria subsection Longirostres and section Dispermae form a distinct clade, (3) twisting of the keel beak is an apomorphy within the genus, (4) there is a reversal to keel beak rostrate-not spirally twisted in C. shevaroyensis and an independent origin of a rostrate-spirally twisted keel beak in C. humilis, and (5) the trifoliolate condition is a plesiomorphy in the genus and the simple leaf condition an apomorphy; there is a single reversal to the trifoliolate condition in C. orixensis. The current morphological classification system of Indian Crotalaria species includes six sections, but these circumscriptions are not supported by the molecular data.