| مستخلص: |
We present data on sexual systems and associated traits in the New Zealand angiosperm flora and discuss reasons for the anomalously high levels of gender dimorphism in the flora, and the low levels of monoecy in woody species. Along with Hawai’i and New Caledonia, New Zealand has exceptionally high levels of gender dimorphism (19.5% of angiosperm species). The plant traits associated with gender dimorphism (woody growth, small, unspecialised white to yellow-green flowers, abiotic pollination, fleshy fruit) are the same as those in other regions and most gender dimorphic species belong to lineages that were already gender dimorphic on arrival in New Zealand. We attribute the high levels of gender dimorphism to several distinct factors. New Zealand’s evergreen forests have many small trees and understorey shrubs with fleshy fruit and small, open, inconspicuous flowers, a combination characterised by high levels of gender dimorphism elsewhere. Many of these species belong to lineages that migrated from the tropical north, a region with high levels of gender dimorphism. In comparison with many other regions, the New Zealand angiosperm flora has few annuals, and few plants with large, specialised flowers or pollinated by birds, traits elsewhere associated with exceedingly low levels of gender dimorphism. Finally, chance may have played a role through the association of gender dimorphism with rapidly radiating lineages. While the New Zealand angiosperm flora has similar levels of monoecy (14.2%) to other comparable regions, monoecy is exceptionally uncommon in the tree flora (3.4% for strictly monoecious species). However, the endemic Nothofagaceae and introduced woody monoecious species thrive in New Zealand. We suggest it is the lack of temperate sources for monoecious tree species, combined with the difficulty large-fruited monoecious tropical species have in crossing ocean gaps that may be ultimate reason for their failure to establish in greater numbers. [ABSTRACT FROM AUTHOR] |
