Pollen Presenter Morphology and Anatomy in Banksia and Dryandra

Abstract

Style shape, and pollen presenter morphology and anatomy, are similar in Banksia L.f, and Dryandra R.Br. There are four style shapes-straight, bowed, s-shaped and hooked. However, in Dryandra, s-shaped and hooked styles are uncommon. The stigma in all cases is contained within the pollen presenter, but there is variation in the location of the stigmatic groove on the presenter, from truly apical (terminal), obliquely terminal to rarely located at the base of the presenter as in B. ericifolia. There is also variation in whether the pollen is deposited over the stigmatic groove in bud or the slit is free of pollen at anthesis. In Banksia, 73% of species studied have the groove covered with pollen, while in Dryandra, a somewhat lower proportion of species (50%) has this configuration. Pollen cohesion on the presenter varies from sticky to loose but is mostly slightly sticky. Similar pollen presenter forms occur in both genera, but in Dryandra, the generally less elaborate shapes are more frequent than is the case in Banksia. Anatomically, the pollen presenters are quite complex, with several cell layers concentrically disposed around the central transmitting tissue. There is considerable variation in the epidermal cells of the presenters between species. In most, the cells are small and thick-walled, but in B. ilicifolia, they are very thin-walled and enlarged into elongated projections. Similar forms occur in other species. In B. tricuspis, the epidermal cells are enlarged, regularly rounded in shape and become smaller and thick-walled near the stigmatic groove. Underlying the epidermis, polyphenol-containing cells and sclerenchyma vary in proportion between species and also in their location within the presenter. The variation in wall characteristics of epidermal cells and the proportion of sclerenchyma in different species is likely to be related to maximising pollination success within an environment containing a variety of pollinator behaviours. Although vertebrates are important in pollinating many species, invertebrates are likely to be the primary pollinators of a significant number of the other species in both genera.