Influence of Leaf Type and Plant Age on Leaf Structure and Sclerophylly in Hakea (Proteaceae)

Abstract

Hakea Schrader (Proteaceae) species possess one of two contrasting leaf morphologies-broad or terete. Terete leaves are either simple (needle-like) or two-or three-pronged, and are further characterised by their greater thickness (> 1 mm), smaller projected area and mass, higher mass per unit area (a measure of sclerophylly) and lower density than broad leaves. Broad leaves are much more variable in their morphology, ranging from narrow-linear to fan-shaped or ovoid-elliptic, and may be flat, undulate, shell-shaped or spiralled. The greater thickness and sclerophylly of terete leaves can be partially attributed to the presence of a prominent, thick-walled parenchyma core and increased palisade thickness. The core contains a compact conduit of fibre-capped vascular bundles. The sclerophyllous nature of broad leaves is due to their high density, attributable to their thin palisade and large fibre caps surrounding the main vascular bundles. Both leaf types have a thick cuticle (> 20 m) in mature plants, and sunken stomates, with terete leaves possessing a greater stomatal density than broad leaves. Both leaf types are isolateral and hence amphistomatous. Within a species, adult and seedling leaves having a similar leaf type differ morphologically rather than anatomically, with an overall increase in leaf thickness and higher levels of sclerophylly in adult leaves. Some species produce broad seedling leaves that are eventually replaced by terete adult leaves.

Selective feeding by kangaroos (Macropus fuliginosus) on seedlings of Hakea species: Effects of chemical and physical defences

“…Others have broad, flat leaves that develop numerous marginal spines (H. oleifolia). Some broad-leaved species, by contrast, possess only small terminal calluses on their leaves (H. elliptica) and appear to lack physical defences (Groom et al 1997). It is not unusual for six or more co-occurring Hakea species to establish after fire, together with regenerating shrubs and grass-like herbs, providing kangaroos with a wide choice of potential food plants.…”

Changes in nitrogen resorption of trembling aspen (Populus tremuloides) with stand development

“…Because soil nutrient availability changes with stand development since stand-replacing fire, and many ecophysiological plant traits have been linked to plant aging (Callaghan 1980;Groom et al 1997), plant nutrient resorption may also change with stand age. However, no study, to our knowledge, has addressed the effects of stand age on plant nutrient resorption.…”

Proteaceae from severely phosphorus‐impoverished soils extensively replace phospholipids with galactolipids and sulfolipids during leaf development to achieve a high photosynthetic phosphorus‐use‐efficiency

“…6). Unlike Banksia species, which commonly have several stomata located in crypts, Hakea species only occasionally have sunken stomata in shallow individual crypts (Groom et al, 1997;Jordan et al, 2008). The absence of deep stomatal crypts with multiple stomata leads to a longer path for CO 2 diffusion from the air to the chloroplasts (Roth-Nebelsick et al, 2009).…”