PALYNOLOGY OF THE GENUS PASSERINA (THYMELAEACEAE) - RELATIONSHIPS FORM AND FUNCTION

Pollen of the genus Passerina L. differs markedly from that of other s outhern African members of the Thymelaeaceae. Grains of most members o f the Thymelaeaceae are characterised by a typical croton pattern, com prising rings of more or less trihedral sexine units mounted on an und erlying reticulum of circular muri. In Passerina, however, the suprate ctal subunits are fused completely to form a continuous reticulum, whi ch replaces the underlying reticulum. The reticulum in Passerina is th erefore secondary in origin and not homologous with the basal reticulu m of typical crotonoid grains in the family. The croton pattern has of ten been used as indication of a possible relationship between the Eup horbiaceae and Thymelaeaceae. Pollen of Passerina is adapted to anemop hily. Grain sculpturing clearly demonstrates secondary derivation of a reticulate pattern from the typical croton pattern, through reduction , aggregation and fusion. Pollen of Passerina represents a climax of a continuum of variation in the exine of pollen in the Thymelaeaceae. A s Passerina is considered phylogenetically advanced in the subfamily T hymelaeoideae, the subtribe Passerininae is raised to tribal rank, nam ely tribe Passerineae.