Wood anatomy of South African Meliaceae: Evolutionary and ecological implications

Abstract

Wood structure in seven South African species of Ekebergia, Nymania, Trichilia and Turraea (Meliaceae) was studied and compared with data for other genera of the subfamily Melioideae to elucidate phylogenetic relationships and pathways of trait evolution in this group and to clarify the ecological significance of some wood characters. Non-septate fibres, the presence of crystals in axial parenchyma and relatively wide (> triseriate) heterocellular rays are the ancestral conditions for Melioideae. A loss of crystals confirms the monophyly of the clade embracing tribe Turraeeae and Pterorhachis. Uniseriate rays are synapomorphic for the Turraeeae+Trichilieae clade with secondary gains of wider rays in the Nymania+Pterorhachis lineage and in some species of Turraea and Trichilia. A close relationship between Nymania and Pterorhachis was also confirmed by their similarity in having small intervessel pits. Trichilia is distinctive by its homocellular rays made of square and upright cells. The close affinity between Ekebergia and Quivisianthe is confirmed by their similar composition of rays that consist only of procumbent cells. Nymania capensis and Turraea obtusifolia share narrower (< 50 μm) and more numerous (> 70 per mm2) vessel lumina than other species; these are adaptive features for their habitat.