Wood Anatomy of the Styracaceae: Evolutionary and Ecological Considerations

Woods of over 40 species representing nine genera of Styracaceae were studied. Features present in most taxa include growth rings, diffuse porosity, combinations of both solitaries and pore multiples, exclusively scalariform perforation plates, opposite to alternate intervessel pitting, imperforate tracheary elements with indistinctly bordered pits, both uniseriate and multiseriate heterocellular rays, and axial parenchyma distributed as a combination of diffuse, diffuse-in-aggregates, and scanty. Prismatic crystals occur in species of the genera Bruinsmia, Halesia, and Styrax, and silica is present in a few Neotropical species of Styrax. The characteristic solitary pore distribution and high scalariform perforation plate bar number of Huodendron are of potential evolutionary significance. The xylem of Lissocarpa differs from the Styracaceae in possessing more highly evolved vessel elements with both simple and scalariform perforations and prominently banded axial parenchyma. The occurrence of simple perforation plates in the wider, earlywood vessel elements, along with an increased pore frequency and decreased vessel element length, in Styrax platanifolius and S. texanus is documented. Both species inhabit seasonally dry habitats of the southwestern United States, thus supporting similar specialisations observed in other plants growing in xerophytic conditions. The apparent variation in perforation plate condition within different geographic varieties of S. officinalis is discussed. Significant correlations of wood anatomical characters and latitude of provenance are present among species of Styracaceae. Increasing latitude is strongly correlated with increased pore and multiseriate ray frequency, and decreased vessel element length and wall thickness. Increasing latitude is less strongly correlated with an occurrence of decreased pore diameter, increased bar number per perforation plate, increased fibre-tracheid and intervessel pit diameter, and increased frequency of uniseriate rays. Weak correlations are also evident between increasing latitude and shorter ray height and narrower, shorter, and thinner-walled fibre-tracheids.