Does pollen form follow function? Effects of stigma type, pollination mode and habitat on pollen morphological traits

Pollen grains display striking morphological diversity, yet the ecological driversunderlying this variation remain poorly understood.2. We tested whether pollen morphology reflects adaptation to pollination mode,habitat moisture and stigma type, three ecological factors that impose selectivepressures on pollen dispersal, desiccation tolerance and hydration dynamics.3. We analysed 13 morphological traits for 1151 Central European angiosperm spe-cies using phylogenetic regression models. Traits included pollen size and disper-sal units, number and type of apertures, coatings and both external and internalfeatures of the exine.4. Insect-pollinated species produced larger, coated grains with thicker exine layersand more reticulate ornamentation, while wind-pollinated species had smaller,smoother grains with thinner walls and more frequent Ubisch bodies. Speciesfrom wetter habitats were more likely to disperse pollen in clumps and showeddistinct ornamentation patterns, but several traits hypothesized to reflect harmo-megathic responses (e.g. aperture number, furrows, opercula) showed no mois-ture dependence. Stigma type also influenced pollen form: dry-stigma specieshad more coatings, thicker exine and more frequent opercula, while wet-stigmaspecies had larger, thinner-walled grains with non-perforate ornamentation.5. Synthesis. Our results support the idea that pollen morphology is functionallyadaptive and shaped by distinct phases of pollen performance: dispersal, environ-mental exposure and stigma interaction. These findings highlight the potential oftrait-based approaches for understanding reproductive strategies in angiosperms