POLLEN PRESENTER MORPHOLOGY AND ANATOMY IN BANKSIA AND DRYANDRA

Style shape, and pollen presenter morphology and anatomy, are similar in Banksia L.f. and Dryandra R.Br. There are four style shapes-straigh t, bowed, s-shaped and hooked. However, in Dryandra, a-shaped and hook ed styles are uncommon. The stigma in all cases is contained within th e pollen presenter, but there is variation in the location of the stig matic groove on the presenter, from truly apical (terminal), obliquely terminal to rarely located at the base of the presenter as in B. eric ifolia. There is also variation in whether the pollen is deposited ove r the stigmatic groove in bud or the slit is free of pollen at anthesi s. In Banksia, 73% of species studied have the groove covered with pol len, while in Dryandra, a somewhat lower proportion of species (50%) h as this configuration. Pollen cohesion on the presenter varies from st icky to loose but is mostly slightly sticky. Similar pollen presenter forms occur in both genera, but in Dryandra, the generally less elabor ate shapes are more frequent than is the case in Banksia. Anatomically , the pollen presenters are quite complex, with several cell layers co ncentrically disposed around the central transmitting tissue. There is considerable variation in the epidermal cells of the presenters betwe en species. In most, the cells are small and thick-walled, but in B. i licifolia, they are very thin-walled and enlarged into elongated proje ctions. Similar forms occur in other species. In B. tricuspis, the epi dermal cells are enlarged, regularly rounded in shape and become small er and thick-walled near the stigmatic groove. Underlying the epidermi s, polyphenol-containing cells and sclerenchyma vary in proportion bet ween species and also in their location within the presenter. The vari ation in wall characteristics of epidermal cells and the proportion of sclerenchyma in different species is likely to be related to maximisi ng pollination success within an environment containing a variety of p ollinator behaviours. Although vertebrates are important in pollinatin g many species, invertebrates are likely to be the primary pollinators of a significant number of the other species in both genera.