Pollen morphology in the ericoid clade of the order Ericales,with special emphasis on Cyrillaceae

Pollen morphology and pollen wall structure in 23 species representing all families of the ericoid clade of order Ericales, i.e. Actinidiaceae, Sarraceniaceae, Roridulaceae, Clethraceae, Cyrillaceae, and Ericaceae, was investigated by means of light microscopy and SEM. The pollen wall of all taxa was found to consist of two solid strata, a tectum and foot layer, separated by a more or less narrow infratectum with granular elements. The three genera of Cyrillaceae were found to differ from each other. In Cyrilla and Cliftonia the pollen is psilate, often more than 20 mum in diameter, spheroidal with an indistinct colpus rim; in contrast, pollen of Purdiaea are rugulate and slightly different between species, smaller and often less than 20 mum in diameter, oblate with a projecting rim reaching over the colpus. In several characteristic features, pollen of Purdiaea is more similar to pollen of Clethra (Clethraceae), than to pollen of Cyrilla and Cliftonia .