Pollen morphology and ultrastructure of Acalypha (Euphorbiaceae)

The pollen morphology of 73 species of Acalypha representing most of the taxonomic diversity in the genus was examined with light and scanning electron microscopy, and 14 species with transmission electron microscopy. Acalypha pollen is small (9–22 μm), subisopolar to isopolar or apolar, and oblate-spheroidal to suboblate in meridional outline. The aperture system is 2-8-colporate, with the ectocolpi short (1–5 μm) and almost equal in length to the endopore diameter. Exine ornamentation is rugulate to microrugulate or areolate with distinct scabrae localized on the margins of the muri or scattered over the pollen surface. These results show that Acalypha pollen exhibits significant variation in size, aperture number, aperture distribution and exine ornamentation, and is not homogeneous as previously reported. Two distinct types, each with two subtypes, were recognized based on tectal ornamentation. Though pollen morphology is inconsistent with a phylogeny based on ITS and ndhF sequence data, it does provide support for subgenera Linostachys and Androcephala and several small clades in the molecular phylogeny.