Diversification and Vicariance of Desert Plants: Evidence Inferred from Chloroplast DNA Sequence Variation of Lagochilus ilicifolius (Lamiaceae)

Arid regions in China, especially Alxa-Helan Mountain Range, are considered one of eight diversification centers within China, which contain a number of endemic genera. This region, designation is supported by Maxent and Domain species distribution model simulations of the ranges of 13 genera, indicated the Alxa of Inner Mongolia to be the most noticeable endemic area. However, this enrichment of diversification and endemism in arid zones has not drawn much attention; and only a few studies have called for conservation for its desert taxa.

Evolutionary history of Lagochilus ilicifolius has suggested that diversification was consistent with aridification and desert expansion during the middle Pleistocene; and Helan Mountains might be suggested as the diversification center of the species. However, previous study of L. ilicifolius was limited to populations in China and lacked distribution areas from Mongolia and Russia, and conclusions were inferred from only two chloroplast DNA (cpDNA) intergenic spacers. In addition to Northern China, L. ilicifolius occurs in southwestern Siberia (Tuvinskaya), southeast Mongolia and Leningrad (presently, St. Petersburg). So, the evolutionary history and biodiversity of L. ilicifolius will be better understood giving full consideration to plants in all distribution areas, including China, Mongolia and Russia.

To document arid Northern China as a diversification center for desert plants, and to better understand the mechanisms of desert taxa diversification, GAO Xiaoyang et al. used five cpDNA spacers (trnL-trnF, rps16, psbA-trnH, psbK-psbI and trnS-trnG) to investigate L. ilicifolius in all distribution areas, including Northern China, Mongolia and Russia.

Phylogenetic analyses showed that L. ilicifolius comprises two distinctive lineages, one distributed in China, and another in Mongolia–Russia. The data confirmed that arid Northern China is a distinctive area with many endemic genera. Biogeographic inferences, based on a Bayesian uncorrelated lognormal model together with molecular dating, suggested that the main diversification within the species occurred in the Pleistocene (ca. 1.38–0.3 Ma), resulting from the transition of the climate of Eurasia to a dry-cold pattern as well as the desertification caused the vicariance of desert plants.

The study was published in Biochemical Systematics and Ecology in August 2014.