Karyotype analysis in nine <i>Uraria</i> Desv. and <i>Christia</i> Moench (Fabaceae: Papilionoideae) species from China

Abstract

The genera Uraria Desv. and Christia Moench are sister genera belonging to the tribe Desmodieae (Fabaceae), and most species are used as important medicinal or ornamental plants. Evolutionary patterns and intergeneric delimitation of these genera have long been controversial. In the present study, the chromosome numbers and karyotypes of six Uraria species and three Christia species were analyzed via the root tip chromosome squashing method towards a better understanding of karyotype evolution. The chromosome numbers observed in Uraria and Christia were 2n=2x=22 and 2n=2x=20, respectively. Analysis of karyotypes resulted in formulas of 20m+2sm (U. crinita and U. lacei), 18m+4sm (U. lagopodioides), 22m (U. picta, U. rufescens, and U. sinensis), and 20m (C. campanulata, C. obcordata, and C. vespertilionis). Cluster analysis conducted using the UPMGA algorithm based on chromosomal and karyotypic parameters revealed that these nine species were divided into two clades, where species of Uraria and Christia each formed a monophyletic clade. In the Uraria clade, U. picta, U. sinensis, U. crinita, and U. rufescens were divided into a subclade, while U. lacei and U. lagopodioides were divided together, showing their close genetic relationships. The taxonomically controversial species, C. campanulata, nested within the Christia clade and showed a close affinity to C. vespertilionis.