Dioecy in the endemic genusDendrocacalia (Compositae) on the Bonin (Ogasawara) Islands
Dioecy in the endemic genusDendrocacalia (Compositae) on the Bonin (Ogasawara) Islands
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小笠原群岛特有属Dendrocacalia（菊科）的雌雄异体
DOI：
10.1007/bf02344232
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发表时间：
1995
影响因子：
2.8
通讯作者：
H. Nagamasu
中科院分区：
文献类型：
--
作者：
Makoto Kato;H. Nagamasu
Dendrocacalia crepidifolia Nakai（菊科千里光族）是小笠原群岛哈哈岛特有的乔木属植物，雌雄异株。雄花与雌花的不同之处在于有一个发育不良的花柱（雌花的花柱从花冠外露，深深分叉）和花药充满可育花粉（雌花的花药缺乏花粉）。雄、雌花的花冠大小和每头小花数相似。这种树栖物种的树冠面积在雌雄植株中也相似。性别比为0.55男性，与0.5无显著差异。两种性别产生的花蜜相似的糖浓度（约。50%）。这些花是由野生蜜蜂（意大利蜜蜂）授粉的，但在蜜蜂被引入并随后成为岛上的主要蜜蜂物种之前，它们被认为是由小的、不那么多毛的地方性独居蜜蜂授粉的。岛上Dendrocacalia的进化被认为是源于近亲繁殖的有害影响，这是geitonogamy植物所固有的。岛上增加的geitonogamy是由于木质增加（即，每株植物的花数增加）和最初依赖地方性蜜蜂授粉，现在濒临灭绝。
Dendrocacalia crepidifolia Nakai (Compositae, Senecioneae), the only species of this arboreal genus endemic to Haha Island in the Bonin Islands, was found to be dioecious. Male flowers differ from female ones in having a stunted style (style in female exserted from corolla and deeply bifurcating) and anthers filled with fertile pollen (anthers in the female lacking pollen). The size of the corolla and number of florets per head were similar between male and female flowers. The crown area of this arboreal species was also similar in male and female plants. The sex ratio was 0.55 male, not significantly different from 0.5. Both sexes produced nectar of similar sugar concentration (ca. 50%). The flowers are pollinated by feral honeybees (Apis mellifera), but they are thought to have been pollinated by small, lesshairy, endemic solitary bees before honeybees were introduced and subsequently became the dominant bee species on the island. The evolution of dioecy ofDendrocacalia on the island is thought to stem from the deleterious effects of inbreeding that are inherent in plants with geitonogamy. The increased geitonogamy on the island has resulted from increased woodiness (i.e., increased number of flowers per plant) and the original dependence on endemic bee pollinators, which are now endangered.