THE POLLEN OF SWEDISH CALLITRICHE (CALLITRICHACEAE) - TRENDS TOWARDS SUBMERGENCE

The pollen morphology of the six Swedish Callitriche L. species was in vestigated using LM, SEM and TEM. The surface ornamentation is reticul ate in C. stagnalis, C. platycarpa, C. cophocarpa and C. palustris wit h supratectal elements in the first three species. The ectexine is red uced in C. hamulata, occurring as scattered granules, but completely a bsent in C. hermaphroditica. None of the species has distinct aperture s but C. cophocarpa and C. platycarpa both have leptomata. The ultrast ructure of the pollen wall in C. palustris shows regions with lamellat ed footlayer and an endexine which may function as apertures. Pollen m orphology is found to be related to pollination biology; species with leptomata sometimes being pollinated through ephydrophily and species with reduced exine being hyphydrophilous.