Variation in position of the nascent generative cell in pollen of hedycarya (monimiaceae)

Abstract

Two of the thirteen species of Hedycarya of the family Monimiaceae have pollen in permanent tetrads. In the New Zealand species, Hedycarya arborea, the nascent generative cell is formed at the distal pole of each grain, but in the Australian species, Hedycarya angustifolia, it arises at the junction of the internal (lateral) and external (distal) wall of each microspore. Synchronous division into vegetative and generative nuclei, within each tetrad of both species, is attributed to the presence of cytoplasmic connections between individual grains. It is suggested that the position of the nascent generative cell in H. angustifolia represents the ancestral condition and that the polar position arose with the evolution of a thickened distal polar exine in H. arborea which produced a broad apertural region encircling this polar cap.