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Staminodes are floral structures occurring in approximately one-third of the angiosperms. These organs often go unnoticed in nature because they may mimic other floral parts. Consequently, their macro- and micromorphological portrayal in the literature is limited. This study presents a detailed descriptive account of staminodes in the Cactaceae, specifically the Plains Prickly Pear, Opuntia polyacanthaHaw., a species with both regular (lacking staminodes) and staminodial flowers. We present the first morphological overview of staminodes in the Cactaceae, rendering a wider perception of the variability in patterns of floral parts in this plant group. Light and scanning electron microscopy revealed that staminodes are complex parts located in the middle and outer androecial whorls and display a wide diversity of shapes and sizes. These staminodes (resembling either stamens or tepals) are considered transitional organs deriving from fertile stamens along the androecial margins via a series of transformations involving gradual widening and amalgamation with tepals. Unlike the typical dysfunctional angiosperm staminodes, pollen viability counts showed that some O. polyacanthastaminodes produce fertile pollen similar in shape and size to regular stamens. The staminodes boost an increase in floral size and diameter in relation to non-staminodial flowers. Thus, larger flower diameter and landing platform combined with added viable pollen from staminodes promote visual attraction for pollinators and reproductive assurance. Because of the presence of fertile pollen, broadening the meaning of the term staminode is discussed along with the putative origin of these appendages.

This study focuses on variation in reproductive systems in Acer(maple) species, and how Acermight 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 Acerwith an emphasis on floral morphometrics of A. ginnalaMaxim., A. tataricumL., and the hybrid A. ginnala× tataricumand (2) present a compilation of the reproductive biology of Acerbased on the literature and online information. Morphometric analyses showed that the hybrid A. ginnala× tataricumexhibits 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 Acerspecies, plus the hybrid, representing only 32.3% of the taxonomic diversity. The reproductive modes of Acerinclude 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 Acerlie in the versatility of sexual systems, diverse modes of maturation of reproductive organs, reproductive success, and the ability to colonise wider areas.