Morph bias in inflorescences and individual plants reduces opportunities for geitonogamy in a monomorphic enantiostylous species

Summary Evolution of enantiostyly, a stylar polymorphism characterised by left‐ or right‐handed flowers, is predicted to counter selfing through disassortative pollen movement. However, in monomorphic enantiostyly, both morphs are present on the same individual, and geitonogamy has been proposed to depend on the morph ratio of an individual. Using the monomorphic enantiostylous Didymocarpus podocarpus (Gesneriaceae), endemic to the Eastern Himalayas, we hypothesised that geitonogamous events would be reduced when plants have a biased morph ratio due to disassortative pollen movement. We first established the natural morph ratios and reproductive compatibilities of the morphs, and next examined the role of morph ratios in pollen movement by recording pollinator visitation patterns using visual observations and quantum dots. Our results show that most inflorescences and plants exhibit a stochastic skew in their morph ratios, while populations maintain an isoplethic ratio. Pollen transfer and pollination success were higher between morphs than within morphs, and inter‐morph pollinator switches within a plant significantly decreased with an increase in morph bias. We show that within a plant, biased morph ratios combined with disassortative pollen movement can limit the occurrence of geitonogamous events, thus providing a mechanism to improve pollination success while also retaining reproductive assurance.