Comparative vegetative development of divaricating and arborescent Sophora species (Fabaceae)

Abstract

Morphometric parameters that have been used previously to define divaricates are not useful for the genus Sophora. In measurements of forest-grown material, only node-angles effectively distinguished between the arborescent S. tetraptera and the divaricating species S. prostrata and S. microphylla. We examined the developmental basis for the generation of divaricating architecture in Sophora species by following growth of potted material over one year. The divaricating form was characterised by a twice-yearly production of new branches; sylleptic outgrowth in the spring, and proleptic outgrowth towards late summer. Branches arose predominantly from the proximal node. By contrast, the arborescent species had only a single growth period, and proleptic branches were produced from more distal nodes. In all three species, growth was most extensive in the uppermost regions of the canopy. Developmental processes may be better descriptors of divarication than shoot dimensions.