Reasons for the Extremely Small Population of putative hybrid Sonneratia × hainanensis W.C. Ko (Lythraceae).

Sonneratia  hainanensis, a species once endemic to Hainan Island in China, is nowendangered. China’s State Forestry Administration lists this species as a wild plant species with anextremely small population. Field fixed-point investigations, artificial pollination, and laboratoryexperiments, as well as other methods, were applied to study the reproductive system and seedgermination of S.  hainanensis to elucidate the reasons for the endangerment of this species.The results are as follows: (1) Outcrossing index, pollen-ovule ratio, and artificial pollinationshowed S.  hainanensis has a mixed mating system and mainly focuses on outcrossing with someself-compatibility. (2) Fruit and seed placement tests showed that the fruit predators on the groundwere mainly Fiddler crab and squirrel, with the predation rates being 100%. The artificially spreadseeds do not germinate under natural conditions. The mean seed destruction rate and remainingrate of were 82.5% and 17.5%.