genus Eugenia (Myrtaceae) in southern Africa: structure and taxonomic value of bark

The anatomy of 60 samples of mature bark representing 12 southern African species of Eugenia s.str. was studied. Bark surface patterns are correlated with internal structure and the taxonomic significance of the bark features is explored. Two bark categories are distinguished. Bark type X [E. capensis (Eckl. & Zeyh.) Sond., E. natalitia Sond., E. simii Duemmer and E. umtamvunensis Van Wyk] is characterized principally by a smooth or weakly dippled-scaly surface, abundant dilatation tissue (pseudocortex) in the inner bark, phellem with one type of phelloid cell and a well-defined phelloderm. Bark anatomy was found to be useful to separate species. Bark type Y [E. erythrophylla Strey, E. verdoorniae Van Wyk, E. woodii Duemmer, E. zeyheri (Harv.) Harv., E. zuluensis Duemmer and three undescribed species] is characterized mainly by a flaky surface, little dilatation growth in the inner bark, phellem with two types of phelloids in the phellem and the lack of a distinct phelloderm. With the exception of E. zuluensis these species cannot be distinguished on the basis of bark features. Bark characters confirm a previously proposed distinction between two supraspecific groups among native species of Eugenia. For diagnostic purposes bark structure is more useful than wood. It is suggested that some of the differences between the two main bark types can be interpreted in terms of the relative rates of formation of xylem and phloem at the vascular cambium.