Wood and bark anatomy of Andriana (Heteromorpheae, Apiaceae) with phylogenetic implications

Abstract

The wood structure was examined in two species of Andriana, and the bark structure in one species of this genus. The Malagasy endemic genus Andriana is similar to the southern African genera of the tribe Heteromorpheae (Apioideae, Apiaceae) in having axial secretory canals arranged in a single ring in the innermost part of the cortical parenchyma and radial dilatation of secondary phloem. This genus is distinctive, however, from the latter by the common presence of column-shaped to bottle-shaped epidermal cells with very thick cuticle. Helical thickenings on vessel walls have not been found in Andriana; thus this feature can be considered a synapomorphic trait only for the Heteromorpha clade rather than for the tribe Heteromorpheae, as it was previously suggested. Surprisingly, secretory canals in the secondary phloem of Andriana species lack sheaths of specialized axial parenchyma. The absence of these sheaths is thought to be unique within the suborder Apiineae, which comprises the families Araliaceae, Myodocarpaceae, Pittosporaceae, and Apiaceae.