Wood samples of 44 specimens representing 34 species and 16 genera were investigated using light microscopy (LM) and scanning electron microscopy (SEM). The wood anatomical terminology follows the ‘IAWA list of microscopic features for hardwood identification’ (IAWA Committee, 1989).
Since all three types of non-perforated tracheary elements, tracheids, fibre-tracheids and libriform fibres, are present in Ericaceae s.l., and intermediate cell types frequently occur in this family (e.g. Baas, 1979), it may be difficult in some instances to determine the true nature of a cell. We consider tracheids to be long and narrow cells, with dense pitting on both radial and tangential walls (approx. 15–50 pits per 100 µm of tracheid length). These pits are distinctly bordered and form two or three longitudinal rows on the radial and tangential walls. Tracheids are relatively rare in epacrids and have usually thin to thick walls. Fibre-tracheids on the other hand, represent the most common cell type of the ground tissue. They are somewhat longer than tracheids, narrow, thin- or thick-walled, and contain a single row of distinctly bordered pits on the tangential walls (approx. 5–15 pits per 100 µm of fibre-tracheid length). The mean distance between two fibre-tracheid pits on the tangential wall is longer than the distance between two tracheid pits, although the pit borders do not differ in size (approx. 3–5 µm). Libriform fibres are extremely rare in epacrids and are about as long as fibre-tracheids. They are narrow, mostly thin-walled, septate or non-septate, and show only few to very few, indistinctly to minutely bordered pits (sometimes also simple pits) on the tangential walls. Pit borders on the libriform fibres are 2–3 µm in size and their density ranges from less than one to four per 100 µm length. Sometimes only two or three pits are observed near the end of libriform fibres. For all measurements of tracheary elements, only clearly identifiable cells were taken into account.
Wood sections of about 25 µm were cut using a sliding microtome. Most of the material collected was derived from thick, mature stems, but wood from very narrow stems (about 2–3 mm in diameter) was examined for genera that produce very little secondary xylem (e.g. Needhamiella, Oligarrhena and Prionotes). Transverse sections (TS) were cut using two pieces of polystyrene foam to support the tiny samples. To make tangential (TLS) and radial (RLS) longitudinal sections of these thin stems, the sample was mounted using superglue on a rectangular piece of wood that was clamped in the microtome holder. The entire thickness of the wood sample could then be used to produce longitudinal sections. After bleaching, staining and dehydrating, tissues were mounted in Canada balsam. The techniques of Jansen et al. (1998) were followed to prepare samples for maceration and SEM. Wood features were plotted on trees using the program MacClade 4.01 (Maddison and Maddison, 2001). Graphics were made with CA CricketGraph III version 1·5.
The wood samples studied are listed in Table 2 with reference to the origin, collector, and the diameter of the wood sample.