Wood Anatomy of Ascarina (Chloranthaceae) and the Tracheid-vessel Element Transition

Quantitative and qualitative features are presented for 13 collections of 8 species of Ascarina. Wood anatomy is maximally primitive in most respects; moderate exception occurs in the imperforate tracheary elements, which range from tracheidlike (A. solmsiana) to fiber-tracheids (septate in two species). Perforation plates are scalariform, average more than 100 bars per plate, and have bordered bars. Even more significantly, portions of the primary walls in perforations characteristically fail to dissolve; these pit membrane portions range from nearly intact (much like the pit membranes in pits on end walls of tracheids of vesselless dicotyledons) to remnant strands or flakes. Dissolution of pit membranes in perforations is apparently inhibited by deposition of resinlike substances in some species; the rugose surfaces formed by these deposits may account for a report of vesturing on vessel walls of Ascarina. Axial parenchyma is diffuse, with only very small expressions of diversification; apotracheal banded parenchyma is, however, present in A. swamyana. Wood of Ascarina is highly mesomorphic. With age of plant, vessels increase in diameter, vessel elements and fiber-tracheids increase in length, and rays become wider and have a higher proportion of procumbent cells; uniseriate rays decrease in abundance. The implications of wood anatomy data on generic distinctions within the family and on the systematic position ofChloranthaceae will be examined when monographs on woods of the other genera have been completed.