Incidences and ecological correlates of dioecious angiosperms in Taiwan and its outlying Orchid Island

Sexual systems, particularly dioecy, and the habit correlations were examined for 3052 native angiosperms in Taiwan and 689 species from its outlying Orchid Island, and compared among different vegetation types. The majority of angiosperms in Taiwan are hermaphrodites (74.4%, N = 2272), followed by monoecious taxa (11.2%, N = 341), and then dioecious taxa (7.9%, N = 240) and polygamous taxa (6.5%, N = 199). The incidence of dioecy in Taiwan (7.9%) and Orchid Island (11.9%, N = 82) exceeded world averages, but was lower than that of most tropical oceanic islands. Dioecy in Taiwan and Orchid Island is strongly associated with woodiness, and is over represented in trees and climbers, but not in shrubs. In woody taxa, 175 of 1,005 (17.4%) taxa are dioecious while only 65 of 2,047 (3.2%) herbaceous taxa are dioecious in Taiwan. The percentages of dioecy decrease with increasing altitude in Taiwan. The percentages of dioecy varied among the six selected vegetation types in Taiwan, from 14.1% in the Linkou Laterite Terrace secondary forest to 23.9% in the Nanjenshan plot, the highest percentage ever found in a forest plot.