Inferring ancestral distribution area and survival vegetation of Caragana (Fabaceae) in Tertiary

Caragana, a leguminous genus mainly restricted to temperate Central and East Asia, occurs in arid, semiarid, and humid belts, and has forest, grassland, and desert ecotypes. Based on the previous molecular phylogenetic tree and dating, biogeographical analyses of extant species area and ecotype were conducted by means of four ancestral optimization approaches: S-DIVA, Lagrange, Mesquite, and BBM. The results indicate the ancestral attributes of Caragana as an arid origin from the Junggar Basin and arid belt of climate and vegetation in the middle Miocene. The ancestral ecotype was most likely adapted to steppe habitats. Uplift and expansion of the Qinghai-Xizang (Tibet) Plateau (QTP) and retreat of the Paratethys Sea are believed to have led to this origin, and also the subsequent diversification and adaptive radiation in the genus. The direction of radiation is suggested in brief to have been from the Central Asian Junggar to East Asia and Tibet.