A comparative study of the reproductive character and genetic diversity of an autogamous Tylophora matsumurae and its progenitor Tylophora tanakae (Apocynaceae-Asclepiadoideae)

Reproductive character and genetic diversity were investigated for an autogamous species of Tylophora matsumurae endemic to the Ryukyu Islands and its progenitor species T. tanakae. Approximately one-fourth of bagged flowers set fruits in T. matsumurae, although no fruits were obtained from bagged flowers in T. tanakae. In situ pollen tube germination was observed with high frequency in all five populations examined in T. matsumurae. Furthermore, in T. matsumurae, anther sacs were not dehisced even at anthesis. These results suggest the highly autogamous nature of T. matsumurae. No allozymic variation was detected in all seven populations examined in T. matsumurae. The phenogram constructed using the neighbor-joining method based on Nei's unbiased genetic distance indicated that T. matsumurae clustered with the Okinoerabu Island population of T. tanakae. The estimated outcrossing rate of four populations of T. tanakae varied from 0.18 to 0.59. It is probable that T. matsumurae had been derived from the predominantly self-pollinating population of T. tanakae, and rapidly enlarged its distribution area.