Wood and Bark Anatomy of Aristolochiaceae; Systematic and Habital Correlations

Abstract

Wood of Aristolochiaceae has vessels with simple petforation plates; lateral wall pitting of vessels alternate to scalariform; tracheids, fibre-tracheids or libriform fibres present; axial parenchyma diffuse, diffuse-in-aggregates, scanty vasicentric, and banded apotracheal; rays wide and tall, paedomorphic, multiseriate only, little altered during ontogeny (new rays originate suddenly as wid~ multiseriate rays); ethereal oil cells present in rays; wood structure storied. All of these features occur in Lactoridaceae and Piperaceae, and support the grouping of Aristolochiaceae with these families and the nonwoody family Saururaceae. Chloranthaceae may be the family next closest to this assemblage. Druses characteristically occur in rays of Aristolochia. Tracheids in Aristolochia may be correlated with the lianoid habit, although Holostylis, a caudex perennial thought close to Aristolochia, also has tracheids. The fibre-tracheids and libriform fibres of Apama and Thottea may be related to the sympodial shrubby habit of those two genera. On the basis of one species each of Apama and Thottea, the genera differ with respect to wood anatomy. The paedomorphic ray structure of all genera of Aristolochiaceae suggests an herbaceous or minimally woody ancestry rather than ancestors with typically woody monopodial habit. Types of bark structure observed in the species surveyed are briefly characterised. Storied wood structure and presence of druses and ethereal oil cells in rays are newly reported for the family.