Pollen morphology of Gaultheria L. and related genera of subfamily Vaccinioideae: Taxonomic and evolutionary significance

The pollen morphology of 86 samples from 84 species of Gaultheria and the closely related genera Chamaedaphne, Craibiodendron, Diplycosia, Eubotrys, Gaylussacia, Leucothoe, Lyonia, Oxydendrum, Pieris, Satyria, and Vaccinium (subfamily Vaccinioideae) was investigated with light and scanning electron microscopy. The tetrahedral tetrads are tri-zonocolporate and range from 22.9 to 51.5 μm in diameter. Exine ornamentation (apocolpia and mesocolpia) of pollen grains is highly variable. Six exine types of apocolpia and five exine types of mesocolpia are distinguished. Viscin threads on the pollen grains of members of Gaultheria are first reported in the study. Colpus length is correlated with both pollen size and colpus maximum width. There is a weak correlation between corolla length and pollen size when the length of the corolla is less than 6 mm. Infrageneric relationships of taxa in Gaultheria are discussed on the basis of pollen data. Pollen morphology is ubiquitously variable at both the species and genus levels. Pollen data support the sister relationships between Satyria and Vaccinium and between Chamaedaphne and Eubotrys of a previously reported molecular phylogenetic analysis. The evolution of pollen characters is traced by character optimization and results discussed. An evolutionary trend of mesocolpium ornamentation within Vaccinioideae from granulate through granulate-rugulate to rugulate is apparent.