POLLEN MORPHOLOGY OF SCHEFFLERA (ARALIACEAE)

Pollen of 48 species of Schefflera was studied by light and scanning electron microscopy. Eight pollen types are distinguished on the basis of sexine sculpturing and structure, apertural shape, and shape and size of the grains. These pollen types correlate well with other data such as the number of carpels, the condition of corolla, infloresence types, and geographical distribution of each species. To determine the evolutionary status of sexine structure, an association between sexine characters and the number of carpels was sought. Assuming polymery of floral parts to be a primitive condition in Araliaceae, the undifferentiated sexine, which occurs in the multicarpellate species, also appears to be primitive. Other unspecialized features include short grains, and non-sculptured, imperforate tectum. Several species in New Guinea and the Solomon Islands belong to this putative ancestral pollen type, from which other types may have been derived.