Flowering phenology and pollination biology of Ceropegia thailandica Meve and Ceropegia suddeei Kidyoo

Abstract

The flowers of the genus Ceropegia have complex structures that involve in pollination mechanism. These structres gynostegium, pollinarium and corona. Moreover, the corolla tube which is inflated at base and the corolla lobes are connate only at tip forming a cage-like structure functions as a trap. When pollinators are attracted to flower, they could be temporarily trapped inside the flower. From previous studies, there are about 18 species in Thailand. Most Thai species have flowers characterized by a long narrow corolla lobe with distinct inflated basal portion. However, some species have a short corolla tube, such as C. thailandica Meve. This characteristic may affect the efficiency of flowers in detaining their pollinators and a different mechanism may be adopted by flowers to achieve their pollination success. Ceropegia thailandica possesses several morphological characters that are similar to those of C. suddeei Kidyoo. Both species are endemic species, the former occurrs in Phu Wau Wildlife Sanctuary, Beung Kan Province, the latter in Phu Phan national park, Sakon Nakorn Province respectively. They are the grass-like perennial herbs with subglobose tubers, linear leaves, single-flowered inflorescences with long peduncle and the terminal part of corolla lobes draw out into long tails and twisted. However, they are a quite difference in the lenth of corolla tube, C. thailandica has short corolla tube while, C. suddeei has long corolla tube. Therefore, it is interesting to compare their pollination mechanism. The results show that the average period for flower development of C. thailandica was 26.2 days, while that of C. suddeei was 25.05 days. The flowers of the two species started blooming in the morning, about 6:00-7:00 A.M. and remained in anthesis until 1-2 days. The effective insect pollinators of C. thailandica and C. suddeei were small flies of the family Chloropidae and Millichiidae. The pollination mechanism of C. thailandica and C. suddeei can be divided into 5 processes: 1) The flowers emitted floral scents to attract their pollinators from long distance, 2) The insect pollinators landed on the middle part of corolla lobe, crawled around the corolla lobe, then fell into the inflated of the flower, 3) While the insect pollinators were detained in the flower, they tried to find nectar present in the nectar cups located near the guide rails and anther, 4) thereby the pollinarium could be attached to the insect’s mounth parts. Likewise, if the insects entered the flower with a pollinarium, the pollinaria could be inserted between the guide rails, resulting in pollination success, 5) After anthesis, the insect pollinators were finally released from the flower. There was a great difference of untrapping mechanisms between C. thailandica and C. suddee. In C. suddeei, the flower reoriented from erect to horizontal positions, owing to bending of the pedicel. Then, the insect pollinators were released from the flowers. In a different way, the pedicel of C. thailandica did not bent down after anthesis, but the flower released the insect pollinators by wilting of the hairs inside the inflated portion of corolla tube. The Pollen Transfer Efficiency (PTE) of C. thailandica and C. suddeei are 0.16 and 0.21 respectively. These values were different from those reported in other Thai species. Interestingly, the flowering phenology prevented geitonogamy. Each individual plant of C. thailandica and C. suddeei, developed flowers in different stages, but each of these flowers bloomed one after another. Therefore, there was only a single flower at anthesis per plant per day. Lastly, it sees that C. thailanddica and C. suddeei could prevent autogamy by pollinarium reconfiguration.