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

Qualitative and quantitative data are presented for 22 collections of 14 species of Hedyosmum. Wood of the genus is primitive in its notably long scalariform perforation plates; scalariform lateral wall pitting of vessel elements; and the low ratio of length between imperforate tracheary elements and vessel elements. Pit membrane remnants are characteristically present to various degrees in perforations of vessel elements; this is considered a primitive feature that is related to other primitive vessel features. Specialized features of Hedyosmum wood include septate fiber-tracheids with much reduced borders on pits; vasicentric axial parenchyma; and absence of uniseriate rays (in wood of larger stems). Ray structure (predominance of upright cells) and ontogenetic change in tracheary element length are paedomorphic, suggesting the possibility of secondary woodiness in the genus. Wood structure is highly mesomorphic