Pollinator attraction and outcrossing strategies in Iris

Iris comprises approximately 280 species with variable floral traits, which makes it an ideal genus for scientific and horticultural research. Although some irises are capable of selfing and clonal reproduction, pollinator-mediated outcrossing still plays an important role in species maintenance and genetic diversity. However, pollinator attraction and outcrossing strategies in Iris have yet to be systematically summarized. In this paper, we describe the pollinator diversity and floral architecture adaptations for animal pollination in irises. On this basis, we introduce how visual and olfactory signals and floral rewards (eg., pollen, nectar, and heat) are presented in Iris to attract pollinators. Before and after pollinator visitation, Iris plants can promote outcrossing by regulating their floral display, spatiotemporal isolation of male and female functions, and post-pollination processes. Furthermore, third-party factors like florivores and resource allocations need to be considered in studies on pollinator attraction and outcrossing in Iris. Future research should focus on hot or controversial issues with the use of advanced techniques like quantitative measurement of floral signals and molecular detection of outcrossing rates, and on large-scale comparison of the modes of plant-pollinator interactions and outcrossing strategies in Iris species.