Dioecy in Wikstroemia pseudoretusa (Thymelaeaceae) Endemic to the Bonin (Ogasawara) Islands
2004 年 55 巻 1 号 p. 55-61
詳細
2004 年 55 巻 1 号 p. 55-61
The sexual mode of Wikstroemia pseudoretusa, endemic to the Bonin (Ogasawara) Islands, was examined and compared with that of W. retusa, distributed widely in the Ryukyu Islands, Taiwan and the Philippine Islands. Although the two species have generally been regarded as hermaphroditic, we found that W. pseudoretusa was actually dioecious and W. retusa was hermaphroditic. In plants of W. pseudoretusa, male flowers usually produced functional pollen grains, and their gynoecium was vestigial and lacked ovules, while female flowers had a functional gynoecium, including an ovule, and their anthers were vestigial and completely lacked pollen grains. Based on the morphological properties of these species and on the occurrence of hermaphroditism in a closely related W. retusa, distributed on the continental islands, the Bonin W. pseudoretusa seems to be an example of dioecy evolving from hermaphroditism within the Islands.
