Timing of Lineage Diversifications and Biogeographic History of Bauhinia Discussed

Aug 21, 2014     Email"> PrintText Size

Bauhinia is a typical genus of pantropical intercontinental disjunction among the Asian, African, and American continents. Recent studies have been revealed that the Caesalpinioideae are an early offshoot of the Leguminosae. Recently, Bauhinia leaves were found in the Upper Miocene deposits from Wenshan, Southeast Yunnan, China. Fossils can provide direct evidence on origin time and migration or dispersal pathways to some extent, which are of special interest in biogeographic discussions when combined with molecular analyses.  

Prof. ZHOU Zhekun and his team of Xishuangbanna Tropical Botanical Garden (XTBG) described a new macrofossil species of Bauhinia from the Upper Miocene Xiaolongtan Formation in Wenshan County, Southeast Yunnan, China. They used morphometrics to investigate the leaf shapes of Bauhinia and to compare the leaf shapes of extant and fossil species. Based on the new fossil record, they combined fossil records and molecular analyses to discuss the timing of lineage diversifications and the biogeographic history of Bauhinia. 

Morphometric analysis demonstrated that the leaf shapes of B. acuminata, B. championii, B. chalcophylla, B. purpurea, and B. podopetala closely resembled the leaf shapes of the new finding fossil. Phylogenetic relationships among the Bauhinia species were reconstructed using maximum parsimony and Bayesian inference, which inferred that species in Bauhinia specieswere well-resolved into three main groups. Divergence times were estimated by the Bayesian Markov chain Monte Carlo (MCMC) method under a relaxed clock, and inferred that the stem diversification time of Bauhinia was about 62.7 million years. The Asian lineage first diverged at about 59.8 million years, followed by divergence of the Africa lineage starting during the late Eocene, whereas that of the neotropical lineage starting during the middle Miocene. 

Their findings illustrated the power of incorporating fossil records and modern plant distribution areas, together with assumptions about stem group age, to better understand the geographic patterns and the possible dispersal routes of plant species. 

The study entitled “New Biogeographic insight into Bauhinias.l. (Leguminosae): integration from fossil records and molecular analyses” has been published in BMC Evolutionary Biology.