Sexual and vegetative reproduction of the sympatric congeners Drosera anglica and Drosera rotundifolia

• The seed production was lower on D. anglica than on D. rotundifolia.
• The production of daughters was more on D. anglica than on D. rotundifolia.
• D. anglica populations were maintained more by vegetative reproduction.
• D. anglica in restricted habitats should be derived from the reproductive strategy.

Two Drosera species, D. anglica and D. rotundifolia, are established in Sarobetsu mire, Northern Japan. D. anglica is an endangered species in Japan because of its small numbers and population sizes, whereas D. rotundifolia is widespread throughout the country. We hypothesized that the reproductive strategies of these species are closely related to the differences in their population dynamics. To test this hypothesis, we monitored the plant size; flower development; daughters, formed by dormant buds; survival; and growth of the two Drosera species in five 300 cm × 40 cm plots in a post-mined Sphagnum peatland in Sarobetsu mire from 2009 to 2011. The two Drosera species maximized their total leaf area in mid-July; all D. anglica individuals flowered at precisely the same time, but D. rotundifolia flowered two weeks after D. anglica. The dormant buds were formed in the late fall of the previous year. Both D. anglica and D. rotundifolia increased their sexual and vegetative reproduction with increasing shoot size. However, seed production was lower in D. anglica than in D. rotundifolia, and the production of daughters was more than three times higher for D. anglica than for D. rotundifolia. These results indicate that D. anglica and D. rotundifolia populations are primarily maintained by vegetative reproduction and sexual reproduction, respectively. Vegetative reproduction does not allow for long-distance migration; thus, D. anglica established in restricted habitats and was characterized by a reduced population size and endangered status. Further, these results suggest that employing very careful management strategies to protect endangered species is important, with particular focus on providing preferable habitats rather than increasing population sizes.