Reassessment of Species Boundaries and Phylogenetic Relationships in the Desmodium ciliare complex (Fabaceae) Using Morphological and DNA Data

Desmodium (Beggar\u27s ticks) is a generally weedy genus of approximately 280 species in the angiosperm family Fabaceae (Subfamily Papilionoideae, Tribe Desmodieae) characterized by indehiscent loments constricted into segments. Within the Southeastern U.S., the Desmodium ciliare group is one of two Desmodium species complexes that have been historically difficult, with much argument about the limits of species and the role of hybridization. There are three commonly recognized species within the D. ciliare group, D. ciliare (Muhl. ex Willd.) DC., Desmodium marilandicum (L.) DC., and D. obtusum (Muhl. ex Willd.) DC., with two supposed hybrids in addition to the three main species involving D. ciliare with D. strictum (Pursh) DC. and D. paniculatum (L.) DC. To test the species boundaries, focused principally on material collected in Mississippi where all of the three putative species occur, principal component analysis (PCA) of morphological characteristics and analyses of both plastid trnL–trnL-F and nuclear ITS DNA were utilized. Based on phylogenetic analysis using 73 ITS and 12 trnL–trnL-F sequences, there was not enough resolution to circumscribe the Desmodium species of Mississippi, including the D. ciliare complex itself. However, a PCA and subsequent MANOVA of relevant vegetative/floral characters (49 used) among 33 individuals of the D. ciliare complex significantly distinguished all three species and two hybrid individuals (D. ciliare × D. obtusum) from each other. The three species in this complex differ morphologically by terminal leaflet length:width ratio, amount of stem/leaf pubescence, and petiole length