Seed germination traits of Trapella sinensis (Trapellaceae), an endangered aquatic plant in Japan: Conservation implications

► We studied the germination traits of the seeds of Trapella sinensis, which is a rare and little studied endangered species of East Asian distribution. ► The seeds of the species have physiological dormancy that is broken by cold stratification. ► Aerobic condition is essential and alternating temperature has been proved to significantly promote the germination. ► Light also promoted the germination. ► We discussed the safe site of the germination of Trapella seeds. ► Anoxia of sediment caused by the eutrophication of water bodies may have caused the population decline. ► Thus, sediment condition is important for the conservation and restoration of the species. We investigated the effects of cold stratification, temperature, light, and oxygen conditions on seed germination of Trapella sinensis Oliver, an endangered aquatic plant in Japan. Seeds had physiological dormancy, and final germination rate increased with an increasing period of cold stratification. Seeds of T. sinensis had an almost absolute requirement for aerobic conditions to germinate. Also, alternating temperatures significantly promoted germination regardless of light conditions, although final germination percentage was twice to four times higher in light under constant temperature conditions. Suitable sites for germination of T. sinensis appear to be shallow water with alternating temperatures and sufficient oxygen and sediment anoxia, caused by eutrophication of water bodies, may have prevented recruitment of T. sinensis from seed.