Phyllode anatomy and histochemistry of four Acacia species (Leguminosae: Mimosoideae) in the Great Sandy Desert, north-western Australia

Acacias are a major component of the vegetation in arid and semi-arid Australia. The anatomy and histochemistry of phyllodes of four Acacia species, i.e. Acacia ancistrocarpa, A. stellaticeps, A. stipuligera, and A. robeorum with distinct phyllode morphologies, native to the Great Sandy Desert in north-western Australia were studied by combining light microscopy, scanning electron microscopy, and various histochemical tests. The aims were to identify anatomical and histochemical features of different species that could contribute to the plants' adaptation to their desert environment. The results showed that phyllodes of A. robeorum were more xeromorphic but less scleromorphic than those of the other three species, and phyllodes of all studied species, except A. robeorum, were more scleromorphic than xeromorphic. Major xeromorphic features as adaptations to drought include thick phyllodesand densely-packed long palisade mesophyll cells. Scleromorphic features are adaptations to low soil P availability and include thick cuticles, abundant sclerenchyma and lignified parenchyma cells. Isobilaterality, amphistomy, dense trichomes, and thick cuticles are likely structural adaptations associated with open vegetation. Histochemical adjustments of the phyllodes are also likely to contribute to the plants’ adaptations to drought.