Leaf development in Aralia elata in relation to the partial-shoot concept

Abstract

Aralia elata (Miq.) Seem. has large bipinnate leaves in which the rachis bears pairs of leaflets in the distal region and pairs of rachillae bearing leaflets in the proximal region. A supernumerary leaflet is also inserted on the rachis adjacent to each rachilla. The rachilla and supernumerary leaflet could perhaps represent an axillary/axillant relationship, in which case the whole leaf would have a notable similarity to a shoot system, and could lend itself to interpretation as a partial shoot system. The development of the leaf has been examined with this in mind. The supernumerary leaflets arise separately from, and later than the rachillae with which they are associated. It is concluded from this and other evidence, for instance the orientation of the plane of dorsiventrality of leaf components, that the resemblance of the leaf to a shoot system is coincidental. However the leaf can be interpreted along lines suggested by classical morphology as an example of a palmate-pinnate leaf, with the addition of reiteration of the palmate element at each cycle of initiation of supernumerary leaflets.