Pollination Syndromes of Chinese Gesneriaceae: a Comparative Study between Hainan Island and Neighboring Regions

The species-rich Gesneriaceae are typically a tropical family in Asia, showing a monophyletic radiation and high endemism in Southwest China and Hainan Island. The Chinese species have diverse floral traits and pollination systems, but the detailed patterns of diversity and possible differentiations between Hainan Island and the Chinese mainland remain unclear. Here, we enumerate the species diversity and proportion of endemics of Gesneriaceae for Hainan Island and the nearby Chinese provinces of Yunnan, Guangxi, Guizhou, and Guangdong. We then investigate the species evolutionary histories and main floral traits to evaluate speciation and pollination syndromes for the island and mainland flora. We recognize 24 (eight endemic) species on Hainan Island, 236 (106 endemic) in Yunnan, 211 (120 endemic) in Guangxi, 97 (28 endemic) in Guizhou, and 60 (20 endemic) in Guangdong. Although Hainan Island harbors fewer species than nearby regions, probably due to its smaller area, its endemic ratio is high, only slightly lower than Guangxi. A phylogenetic tree based on nuclear ITS 1/2 and chloroplast Trn L-F indicated most Hainan-endemic species were genetically close to species from Southeast Asia, rather than mainland China. For most floral traits, e.g., growth form, corolla type and color, Hainan Island species show no differences from other regions. Hainan Island and Yunnan Province have equal proportions of species with four or two stamens, whereas most species in other regions have two stamens. Hainan Island has a much higher percentage (21%) of actinomorphic species than other regions (< 10%). Most species in Hainan Island have exserted stamens, while stamens are included in most species in other regions. We did not find any increased tendency in floral traits that promote selfing for the island flora. Generalist pollination mechanisms, supported by characters such as actinomorphic corolla, appear to provide sufficient reproductive assurance in pollinator-depauperate Hainan Island.