Comparative bark anatomy of Bursaria, Hymenosporum and Pittosporum (Pittosporaceae)

Nilova, M. & Oskolski, A.A.: Comparative bark anatomy of Bursaria, Hymenosporum and Pittosporum (Pittosporaceae) — Plant Div. Evol. 128: 491–500. 2010. — ISSN 1869-6155. Bark anatomy in 3 species of Bursaria, 9 species of Pittosporum, and in the single species of monotypic genus Hymenosporum (Pittosporaceae) was examined. The members of these three genera resemble Araliaceae, Myodocarpaceae and Apiaceae in the occurrence of axial secretory canals in cortex and secondary phloem, the pattern of alternating zones in secondary phloem, and the absence of fibres in this tissue. We therefore confirm a relationship between Pittosporaceae and other Apiales (van Tieghem 1884, Dahlgren 1989, Takhtajan 1997, Plunkett et al. 1996, 2004) rather than its traditional placement into Rosales (Cronquist 1981). Hymenosporum differs markedly from Bursaria and Pittosporum in the presence of primary phloem fibres, in the cortical (vs subepidermal) initiation of the periderm and in the occurrence of numerous (more than 25) sieve areas on compound sieve plates. These features confirm the isolated position of Hymenosporum within Pittosporaceae, as suggested both by traditional taxonomy and gross morphology (Cayzer et al. 2000) and by molecular phylogenetics (Chandler et al. 2007).