A New Pollen Type in the Winteraceae

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Abstract
Pollen of Zygogynum balansae and Z. pomiferum is described with the aid of the scanning electron microscope. Other members of the primitive ranalean family Winteraceae hitherto investigated have pollen in permanent tetrads, but these two species have solitary grains. Sculpturing is similar on the distal and proximal faces of each grain, excluding the distal apertural zone. The exine pattern resembles that on distal faces of tetrads of other Zygogynum species investigated, including Z. bailloni, the pollen of which is illustrated. Although Zygogynum and Exospermum have rather similar pollen, with sculpturing differing from other Winteraceae in consisting of a less coarse reticulum, pollen of Exospermum stipitatum is clearly distinct from the Zygogynum species investigated, as seen in the scanning electron microscope. It is not clear whether or not the solitary pollen type has evolved from the tetrad form.