Wood anatomy of the Combretaceae

The wood anatomy of all genera of the Combretaceae (Meiostemon excepted) is described in detail on the basis of 120 samples representing 90 species from 19 genera. Additional data from the literature are added. The structural variation of the vestured pits is described and classified. There are two main types, of which the distribution follows the subfamily classification. Considering the overall wood anatomy, the recognition of two subfamilies: Strephonematoideae (Strephonema only) and Combretoideae (all remaining genera) can be supported. Strephonema stands out on account of its fibre-tracheids, type of vesturing and parenchyma distribution pattern. Within Combretoideae, one group of genera (subtribe Combretinae sensu Exell & Stace) stands out markedly on account of their radial vessels, a unique feature not known to occur in any other plant group, and two distinct size classes of vessel elements. The remaining genera, belonging to the tribe Laguncularieae and subtribes Terminaliinae and Pteleopsidinae of tribe Combreteae show a wide overlap in wood anatomical features. The Laguncularieae differ in the ratio of vessel member to fibre length, Terminaliinae and Pteleopsidinae cannot be separated wood anatomically. Although difficult to interpret phylogenetically, arguments are brought forward to consider Strephonema as having the most primitive wood structure and the Combretinae to have the most derived wood. Variation in some quantitative characters such as vessel member length is shown to be at least partly correlated with ecological conditions of the taxa involved. Wood anatomical differences between lianas and erect species are discussed. Synoptical keys to the genera of the Combretaceae and to the species studied of Terminalia are given.