Evidence of the morphological range, transition and evolution of stomatal protection mechanisms in some selected Proteaceae

Xero- and scleromorphic adaptations are obviously shown by Australian plants, in response to the Australian climate and edaphic factors. Since these adaptations overlap, there are problems separating the two. Some qualitative hypotheses about the distinction between xero- and scleromorphic characters have been proposed. This research is an effort to quantitatively determine xeromorphic characters in some members of the Proteaceae, in order to elaborate upon some of the existing hypotheses about these characters. Twenty three species of Banksia, 16 species of Grevillea and 6 species of Orites were sectioned and observed under the light micrscope and measurements were made of the stomata! depressions, margin recurvations, cuticle thickness and hair dimensions. Cuticle peels were made in order to count the number of stomates and hairs on the leaf surface. From the characters measured the following were calculated: the depression index (Id), recurved margin index (Irm), epidermis index (le), hair. index _ (Ih) and cuticle components. The sum totals of the calculations were called the stomata! protection component (Spc). These data were then analysed using an analysis of variance with five replicates per species, in order to investigate whether there were any differences in characters determined .among species observed. Every index calculated (Id, Irm, Ih, le) and the cuticle components were analysed separately, with the aim of determining the intensity of the association between the characters observed and the minimum of the range of habitat annual rainfall, the maximum of the range ·of habitat annual temperature, the maximum of the range of habitat daily radiation and the maximum of the range of maximum daily wind run. An analysis of correlation was applied to these data. A similar method was applied for observations on juvenile and adult leaves. On the basis of these results the possible evolution of Banksia is reconstructed. Results showed that in Banksia species stomata! depression seems to have an important role protecting the stomates from the effect of habitat climatic factors, especially from temperature and radiation effects. The presence of recurved margins and hairs, however, were not as important as stomata! depressions. In Grevillea species, cuticle characters had a significant role in stomata! protection, particularly the stomata! and lower epidermis cuticle. A _contradictory finding to that of Banksia in this genus was that stomata! depression did not contribute to the stomata! depression. In comparison to the two genera already discussed, Orites was quite different. However, the hairs had a significant contribution in protecting stomates from temperature and radiation effects. - The phenomenon of leaf transition from juvenile to adult in some species observed showed some performance similarities to plants grown in harsh environments. Banksia blechnifolia leaves exhibited more intense stomata! depression and denser leaf hairs in adult leaves. It was assumed that these structures increased stomatal protection from excessive radiation. Similar growing phenomena were displayed by leaves of Grevillea pyramidalis. Stomata! depression in this species developed from being not present to being present and then deepened in later leaves. In addition, leaf hairs showed a gradual alteration in density from seedling through juvenile and adult leaves. However, leaves of B. marginata did not show the presence of stomata! depressions either in juvenile or adult stage. The leaf hairs, however, exhibited similar phenomena to those found in B. blechnifolia and G. pyramidalis. The results suggest that stomatal depression, margin recurvation, leaf hairs and cuticle characters increase stomata! protection either individually or collectively. It thus can be concluded that there is a possibility that these characters are xeromorphic when expressed by Banksia, Grevillea and Orites species