Floral morphology and reproductive biology in selected maple (Acer L.) species (Sapindaceae)

This study focuses on variation in reproductive systems in Acer (maple) species, and how Acer might be a useful genus for understanding floral morphology and the evolution of these highly variable systems. The goals were (1) to conduct a survey of reproductive characters in the genus Acer with an emphasis on floral morphometrics of A. ginnala Maxim., A. tataricum L., and the hybrid A. ginnala × tataricum and (2) present a compilation of the reproductive biology of Acer based on the literature and online information. Morphometric analyses showed that the hybrid A. ginnala × tataricum exhibits intermediacy in vegetative morphology and some floral traits compared to the parents. Literature and an online survey revealed some information on the reproductive biology of 40 Acer species, plus the hybrid, representing only 32.3% of the taxonomic diversity. The reproductive modes of Acer include monoecy, dioecy, trioecy, andromonoecy, androdioecy, and andropolygamy, with a trend towards unisexuality. Temporal patterns of maturation of reproductive parts revealed duodichogamy, heterodichogamy, simultaneous, and dichogamy. The pollination syndrome is entomophilous, anemophilous, and ambophilous. We conclude that the evolutionary and geographic success of Acer lie in the versatility of sexual systems, diverse modes of maturation of reproductive organs, reproductive success, and the ability to colonise wider areas.