Notes on the taxonomic and ecological significance of bark structure in the genus Virgilia (Fabaceae, Podalyrieae)

A comparative study of bark anatomy of all three taxa of the genus Virgilia has revealed interesting differences relating to the taxonomic relationships of the species and subspecies and also to the marked ecological differences (as reflected in the bark anatomy) between Virgilia oroboides subsp. oroboides (exposed to high fire frequencies in the western parts of the Cape Province of South Africa, from Cape Town to Swellendam) and V. oroboides subsp. ferruginea and Virgilia divaricata (growing in areas of relatively low fire frequency along the southern Cape coast from George to Port Elizabeth). The conspicuous difference in the appearance of the bark (thick and corky in V. oroboides subsp. oroboides; thin and smooth in V. oroboides subsp. ferruginea and V. divaricata) results from a distinct difference in the sclerification of periderm cells. Detailed descriptions of the bark anatomy of all three taxa are presented, showing a pattern of variation that supports the delimitation of species and subspecies. The discovery of crystals in the trichome cells of V. oroboides subsp. ferruginea appears to be a first record of the presence of crystals inside trichomes in the Fabaceae and is a useful diagnostic character for the subspecies. A remarkable feature of the bark of Virgilia is the common occurrence of acicular crystals arranged in radial (sheath-like) aggregates.