Wood Anatomy of Tasmannia

Quantitative and qualitative data are presented for 11 collections of eight taxa. Diameter and length of tracheids are related to plant size, but populations in cooler locations have narrower and shorter tracheids than one would expect on the basis of plant size and age, and smaller tracheids are believed to be of selective value in these environments because of their resistance to embolisms. Vesturing is absent from tracheids in taxa from warmer localities but pronounced in colder places; this, too, is a probable mechanism for resistance to embolism formation. Helical thickenings are reported for one collection of T. insipida; these thickenings, otherwise known in the family only from Pseudowintera, may play a role similar to vesturing. Scalariform pitting on end walls of tracheids occurs during the first three years of secondary xylem formation, and may also occur after cambial trauma. Axial parenchyma is scarce to absent, and diffuse when present. Rays in Tasmannia wood have relatively few procumbent cells. A summary wood description for the family is presented, and a key to the eight genera is given. Although wood anatomy does contain some features of generic value, data from floral morphology, pollen structure, and leaf anatomy more strongly support the recognition of eight genera. Some species have very distinctive features, but genera are difficult to define; pending acquisition of chemical data, eight genera may be provisionally recognized. The only feature considered as a possible phylogenetic trend in wood within the family is an increased tendency for alternate pits to supplant scalariform pits on end walls of tracheids. Tracheids of Winteraceae demonstrate that scalariform pitting is pervasive and preserved in a flexible way; alternate pits are hypothesized to have been evolved in the family for increased wall strength. Ecological correlations, presented for the entirety of the family, are much like those shown within Tasmannia