The Pollen of SwedishCallitriche(Callitrichaceae) - Trends Towards Submergence

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Abstract
The pollen morphology of the six Swedish Callitriche L. species was investigated using LM, SEM and TEM. The surface ornamentation is reticulate in C. stagnalis, C. platycarpa, C. cophocarpa and C. palustris with supratectal elements in the first three species. The ectexine is reduced in C. hamulata, occurring as scattered granules, but completely absent in C. hermaphroditica. None of the species has distinct apertures but C. cophocarpa and C. platycarpa both have leptomata. The ultrastructure of the pollen wall in C. palustris shows regions with lamellated footlayer and an endexine which may function as apertures. Pollen morphology is found to be related to pollination biology; species with leptomata sometimes being pollinated through ephydrophily and species with reduced exine being hyphydrophilous.