DIVERSE NODAL ANATOMY OF THE CUNONIACEAE

A comprehensive study of nodal anatomy of the Cunoniaceae has revealed an unusually diverse assemblage of nodal types, including patterns with "split-lateral" traces previously undescribed for dicotyledons. On the basis of leaf arrangement and nodal vascularization, six distinct nodal conditions are recognized in the family. The trilacunar, three-trace pattern is the ancestral type from which the multilacunar condition evolved by amplification in the number of lateral traces. The "split-lateral" condition, distinguished by the fusion of lateral leaf traces of adjacent leaves, or the bifurcation of a single trace, and their association with a "common gap," probably evolved concomitant with the transition from opposite to whorled leaves. The characteristic interpetiolar stipules of the Cunoniaceae are vascularized by veins originating from lateral leaf traces, or by a combination of complete lateral traces and veins arising from lateral leaf traces. Both Aphanopetalum and Bauera possess unilacunar one-trace nodes. The most satisfactory family placement of both genera remains uncertain, although the unilacunar nodes of Bauera can reasonably be interpreted as a case of reduction from the trilacunar pattern in response to reduced plant size.