Sexual selection is a mechanism of evolution in which members of one sex choose mates of the other sex to mate with (inter-sexual selection), and compete with members of the same sex for access to members of the opposite sex (intra-sexual selection). It is an accepted concept in animal evolution, but it is more controversial in botany. Sexual selection in plants could work through two principal mechanisms:
- Intra-sexual (male–male) competition: Competing pollen donors vie for ovule fertilization via traits such as pollen packaging, timing of release, and flower morphology.
- Female or pistil-mediated mate choice: Post-pollination filters—such as pollen-recipient compatibility, pollen-tube growth rates, and selective seed abortion — enable differential siring success.
These two mechanisms are, in theory, the main driving forces of sexual selection in flowering plants and their potential relevance to botany is clear, but more complicated than in zoology. The complexity of applying the concept of sexual selection to plants arises from the facts that most plants are hermaphrodites and are non-sentient, meaning that the more obvious elements of female choice (e.g. aesthetic judgements on male secondary sexual characteristics) do not apply. The research challenge currently facing botanists is mainly an empirical one — it involves addressing in a comprehensive way the "empirical question of how often these processes have actually shaped plant evolution in important ways."
