Wood anatomy of Actinostrobus (Cupressaceae)

The wood anatomy of the Western Australian species Actinostrobus arenarius (Cupressaceae) is described for the first time and its features are compared with those of the two other species in the genus: A. acuminatus and A. pyramidalis. Mature heartwood in A. arenarius is light-brown in colour and has an air-dry density of 0.56 g/cm³. Average tracheid length is 4.3 mm. A very prominent warty layer, with individual warts commonly greater than one micron in height and large enough to be visible to light microscopy, lines the inner walls of tracheids. Callitroid thickening is commonly present in narrow (latewood) tracheids, but is absent from wide ones (earlywood). Axial parenchyma cells with dark-red resinous inclusions are tangentially zonate in earlywood. Bordered pitting in earlywood and latewood is uniseriate. Pit borders are circular and there is a raised torus. Average ray height is low. Cross-field pitting is cupressoid and the number of pits per cross field ranges from two to five, with a mean of 3.1. Average ray heights, ray frequencies, ray volumes, and numbers of pits present in cross fields are higher in A. arenarius than in A. pyramidalis, thus supporting the classification of A. arenarius as a separate species within Actinostrobus. Veins of distorted xylem cells, similar in appearance to 'frost rings' occur sporadically in the stems of all three species. If such rings are confined to Actinostrobus, then the combination of a very prominent warty layer, and the common occurrence of frost rings could provide a means of separating Actinostrobus from Callitris. Validation of this scheme requires further research to determine if such rings commonly occur in Callitris.