Vascularization of a Multilacunar Species: Polyscias Quilfoylei (Araliaceae) Ii. The Leaf Base and Rachis

Abstract

Multiple leaf traces depart the stem vasculature at a node to form the rachis vasculature of the odd‐pinnate leaf of Polyscias quilfoylei. The median (M) trace departs the vascular cylinder directly, but the converging lateral traces follow acropetal, oblique pathways through the en‐sheathing leaf base. The leaf traces are partitioned into sub‐bundles within the leaf base, and some sub‐bundles merge with others to form composite bundles. Most mergers in the leaf base occur among sub‐bundles of adaxial and lateral traces; cross‐overs of bundles from opposite sides of the M‐trace are infrequent. The rachis vasculature distal to the leaf base is similar in structure and appearance to that of the stem. Vascularization of the leaflet pair at each rachis node involves partitioning and reaggregating of the trace sub‐bundles. However, these processes are more extreme and bundle cross‐overs are more frequent at rachis nodes than at the leaf base. At the more distal rachis nodes, lateral traces situated nearer the M‐trace contribute to leaflet vascularization. The M‐trace contributes sparingly to vascularization of lateral leaflets; it forms that part of the midvein that extends to the extreme lamina tip of the terminal leaflet.

Leaf Vascular Pattern Formation.

“…In dicot taxa with large leaves or with sheathing leaf bases, additional leaf traces are present, each derived from a different sympodial bundle (Larson, 1986). In grasses, leaf traces are more numerous (equivalent to the total number of large and intermediate veins) but connect in a similar way to independent stem vascular bundles (Sharman, 1942).…”

“…Detailed analyses of the interconnections between leaf traces, midvein, and secondary veins have been made for only a handful of species (Larson, 1975(Larson, ,1984(Larson, ,1986Isebrands and Larson, 1980). In these examples (all woody trees), the provascular strands of the lateral leaf traces extend into the leaf base one to two plastochrons after the median trace.…”

“…In these examples (all woody trees), the provascular strands of the lateral leaf traces extend into the leaf base one to two plastochrons after the median trace. Shortly thereafter, additional provascular strands, the subsidiary bundles, appear at the leaf base and extend both acropetally into the leaf primordium and basipetally to connect with stem vasculature (Larson, 1975(Larson, , 1984(Larson, , 1986. In the simple leaves of Populus, midvein components remain discrete, so that dista1 secondary veins are derived from the central and lateral leaf traces, midsecondaries are derived from lateral and subsidiary trace elements, and basal secondaries are derived from the last-formed subsidiary traces (Isebrands and Larson, 1980).…”