Evolution of pollen morphology.

Over evolutionary time, the morphology of angiosperm pollen has evolved toward an increasing number of apertures, among other things. From a neo-Darwinian point of view, this means that (i) some polymorphism for aperture number must exist and (ii) there must be some fitness increase associated with increasing the aperture number. Pollen types with different aperture numbers often occur in the same species. Such is the case in Viola diversifolia. Comparison of pollen with three and four apertures in this species showed that four-apertured grains germinated faster than three-apertured ones but that the four-apertured ones experienced other disadvantages. These results obtained on the gametophyte can be interpreted in terms of strategies of the sporophyte.