Wood and bark anatomy of South African Picrodendraceae with systematic and ecological implications

Abstract

Wood and bark structure of Androstachys johnsonii and Hyaenanche globosa (Picrodendraceae) is described. Two species share simple perforation plates, minute to small intervessel pits, and nonseptate fibres; these traits also reported in other Picrodendraceae. Androstachys is distinctive in having scanty paratracheal axial parenchyma and uniseriate rays with vessel-ray pits restricted to marginal cells. Bordered pits on fibre walls is an ancestral condition for the African Picrodendraceae. High vessel frequency and vessel grouping in Androstachys can be adaptive for semi-arid climate with wet summer. Both genera share the subepidermal phellogen initiation and the presence of thick-walled fibers and sclereids in secondary phloem. In Hyaenanche, the bark is dilated by stretching and divisions of parenchyma cells with formation of pseudocortex. Androstachys shows no ray dilatation, but sclerification of its parenchyma can make substantial contribution in bark expansion. Abundant trichomes on epidermis of young shoots of Androstachys are presumably involved in the water uptake from mists.