Two of the thirteen species ofHedycaryaof 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 inH. angustifoliarepresents the ancestral condition and that the polar position arose with the evolution of a thickened distal polar exine inH. arboreawhich produced a broad apertural region encircling this polar cap.
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