Different Flowering Strategies Ensure Reproductive Success in Two Coexisting Self-Incompatible Orchids

Orchids have evolved diverse reproductive strategies to overcome pollinator limitation and pollen discounting from geitonogamy, particularly in self-incompatible species. This study compares two coexisting, self-incompatible orchids (Pholidota articulata and Coelogyne prolifera) sharing pollinators in an ancient tea garden, examining how their contrasting flowering strategies enhance reproductive success. We conducted a 3-year study analyzing flowering phenology, floral traits, pollinator behavior, pollinia removal and deposition, the breeding system, and fruit set under both natural conditions and from hand-pollination treatments. Despite partial flowering overlap, the species exhibited distinct strategies: P. articulata employed a mass-flowering strategy with large floral displays, high nectar rewards, and synchronized anthesis (all flowers per inflorescence opening within ~4 days), while C. prolifera adopted a steady-state strategy with prolonged single-flower longevity (~13 days) and extended flowering duration (60 days) and consistent but comparatively lower nectar secretion. Both species shared two pollinator species (Vespa velutina and Vespa mandarinia) in 3 years, but the visit frequency was consistently higher for P. articulata. Remarkably, 83.3% ± 6.5% of P. articulata flowers were pollinated on their first day versus only 4.5% ± 8.6% in C. prolifera. Although pollinia removal and deposition peaked during initial anthesis in P. articulata, C. prolifera showed lower pollen discounting (44.4%) throughout flowering. Despite these differences, both maintained moderate natural fruit sets (21.2%-30.7%) across years, which are substantially higher than the typical 2% reported for most self-incompatible orchids. Our findings demonstrate that coexisting, self-incompatible orchids sharing pollinators can achieve comparable reproductive success through divergent strategies: P. articulata maximizes pollination efficiency via synchronized mass-flowering, while C. prolifera enhances pollination opportunities through prolonged flowering. This highlights the adaptive diversity of flowering strategies in self-incompatible orchids facing pollinator limitation and geitonogamy.