Alkaloid polymorphism and ITS sequence variation in the Spiraea japonica complex (Rosaceae) in China: traces of the biological effects of the Himalaya‐Tibet Plateau uplift

Spiraea japonica , a diverse, perennial shrubby species complex widespread across E Asia, was a useful model in a first attempt to link specific phylogeny, floristic evolution, and historical environmental changes in E Asia. DNA‐based phylogenetic reconstruction served as a framework to investigate whether the patterns of variation in alkaloids and nrITS from varieties of S. japonica reflect the geological history of China and the uplifting of the Himalaya‐Tibet plateau, the most significant geological event in E Asia since the late Paleocene. The high geographical structure found in the phylogenetic trees was corroborated by the distribution of alkaloids. All populations from E China, with mainly hetisine‐type alkaloids, formed a single clade, sister to a clade of all populations from SW China, with mainly atisine‐type alkaloids. The distribution boundary between the two clades roughly matched the floristic division between the Sino‐Japanese Forest and the Sino‐Himalayan Forest subkingdoms, as well as the environmental division between SW and E China, suggesting a close link between specific phylogeny, floristic evolution, and geographical changes in E Asia. The divergence between lineages at variety and population level within the eastern clade was slightly older than those within the southwestern clade, supporting the hypothesis of a northeast–southwest migration of Spiraea since the Eocene. The uplift of the Himalaya‐Tibet plateau and subsequent increase in geographical complexity in SW China, could facilitate divergence maintenance, thus accelerating the evolutionary rate.