Pollination biology of the rare and endangered submerged plant, Ottelia cordata

Abstract

Ottelia cordata is a kind of rare and endangered submerged plant that grows in freshwater wetlands in northern Hainan Island, from Haikou to Wenchang in China. This species is known for its beautiful appearance and the distinct “flower river” landscape, which makes it a high ornamental value. With the intensification of human activities, the habitat of O. cordata has been sharply reduced and fragmented, leading to its endangerment. In order to explore the reproductive characteristics and reproductive laws of O. cordata, the flower morphology, sex ratio, pollen viability, stigma receptivity, reflectance spectrum, pollen limitation and apomixis, and the types and behaviors of pollinators in O. cordata were analyzed. That is, the pollination biology of O. cordata were studied for its further in-situ and ex-situ conservation. The results were as follows: (1) The flowers were dioecism, and the sex ratio of female and male individuals was about 1∶2; the morphologies of male and female flowers were similar, and the female flowers were slightly larger than the male. (2) O. cordata had high pollen viability and stigma receptivity in budding and blooming phases. (3) Apis cerana was the main pollinator of Ottelia cordata, which visited male flowers more frequently than female flowers, with higher pollination efficiency. (4) The distance between the color loci of pistils and stamens was significantly higher than the discrimination threshold of Apis cerana. (5) The fruit setting percentage under natural pollination was similar to that under artificial pollination (95.29% and 98.42%, respectively), and there was no apomixis and low pollen limitation in the natural population of Ottelia cordata. In conclusion, the deceptive pollination of O. cordata simulated by both sexes is imperfect. Pollinators can visually distinguish female and male flowers. However, the large number of male flowers of O. cordata attracted many insects to visit flowers, which increases the probability of “mistake” pollination and is enough for the reproductive needs of female flowers. Therefore, future ex-situ conservation and artificial population restoration should pay more attention to population size, sex ratio and the number of local pollinators.

Keywords

• dioecism
• deceptive pollination
• breeding system
• pollen limitation
• hydrocharitaceae