High species diversity within a geographic area may be attributed to either recent rapid speciation in a 'cradle' or the gradual accumulation and preservation of species over time in a 'museum'.  

China, home to 30,000 species of the approximately 350,000–400,000 species of vascular plants, is ideal for investigating patterns of biodiversity.  

Whether areas within China serve as cradles or museums remains unclear, as floristic components of putative ancient origin and recent diversification have both been discovered. 

Using a dated phylogeny of 92% of the angiosperm genera for the region, a nearly complete species-level tree (26,978 species), and detailed spatial distribution data, researchers from Institute of Botany of the Chinese Academy of Sciences have investigated the spatio-temporal divergence patterns of the Chinese flora. 

Divergence time estimation shows that ca. 66% of the angiosperm genera in China did not originate until the early Miocene, and the herbaceous genera have diversified much more rapidly than the woody genera during the past 30 million years. 

The analyses of spatial divergence indicate that the flora of eastern China (particularly in central to southern China) bears a signature of older divergence, phylogenetic overdispersion (spatial co-occurrence of distant relatives), and higher phylogenetic diversity.  

By contrast, the flora of western China shows more recent divergence, pronounced phylogenetic clustering (co-occurrence of close relatives), and lower phylogenetic diversity.  

These patterns are also observed in analyses of phylogenetic diversity based on multiple species-level trees using simulated branch lengths.  

Researchers also found that a much higher percentage of herbaceous than woody genera has originated during the past 30 million years in western China. However, both herbaceous and woody genera diverged at similar rates throughout geological time in eastern China.  

The study suggests that eastern China represents a floristic museum, and western China an evolutionary cradle, for herbaceous genera; eastern China serves as both a museum and a cradle for woody genera. 

The research team found that phylogenetic diversity hotspots are mainly located in several provinces of eastern China (i.e., Guangdong, Guangxi, Guizhou, Hainan, and Yunnan). These areas are also hotspots for threatened plants in China, as inferred by previous studies.  

These results suggest the need to establish more connections between existing nature reserves and national parks that span provincial borders to conserve plant lineages of ancient and recent origins in eastern China, as well as the other organisms that depend on these floristic elements. 

This study has been published in Nature as a letter entitled, "Evolutionary history of the angiosperm flora of China".  

The research was led by Dr. CHEN Zhiduan's team at the Institute of Botany, Chinese Academy of Sciences (CAS), in collaboration with researchers from Nanjing Forestry University, University of Florida, Hope College, University of Michigan, Chengdu Institute of Biology, CAS, and Australia National Herbarium. 

The study was supported by the National Key Basic Research Program of China, the National Natural Science Foundation of China, the Chinese Academy of Sciences International Institution Development Program, the US National Science Foundation, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.