Pollen aperture evolution - a crucial factor for eudicot success?

Increased aperture number in angiosperm pollen grains offers a potential selective advantage because it increases the number of prospective germination sites, thus facilitating contact between at least one aperture and the stigmatic surface. Such an increase occurred at the base of the eudicot clade, coupled with an apparently fundamental shift in aperture position from polar to equatorial. This transition could represent a key innovation underlying eudicot success and subsequent radiations. There is a general trend in angiosperms to an increase in pollen aperture number, suggesting that pollen apertures are under strong selection pressure. This trend can be observed by comparing the aperture patterns in basal angiosperms (including monocots) with those of eudicots. Different developmental strategies operate for pollen apertures in basal angiosperms and eudicots; the eudicot strategy has been more successful in generating higher aperture numbers.