The systematic significance of bark structure in southern African genera of tribe Heteromorpheae (Apiaceae)

The bark anatomy of five southern African genera of tribe Heteromorpheae (Apiaceae) has been investigated: Anginon (eight species), Glia (one species), Heteromorpha (two species), Polemannia (two species) and Dracosciadium (one species). They are all similar to other members of the order Apiales and share with them the presence of secretory canals in both the cortex and secondary phloem, the presence of two types of axial parenchyma and the absence of fibres in the secondary phloem. The bark of Heteromorpheae typically has a narrow cortex with secretory canals arranged in one ring and radial dilatations of the secondary phloem, but these character states also occur in other genera of the family. The most remarkable differences between the genera are the appearance of the bark surface, the periderm structure, the presence of primary phloem fibres, the length of sieve tubes and sclerification of the axial parenchyma in collapsed secondary phloem. The trunks of Heteromorpha and Polemannia have translucent phellem and chloroplasts in the phelloderm cells, allowing the stems to photosynthesize. The shape of the epidermal cells, the presence of trichomes and the occurrence of secretory canals in the secondary phloem rays can be used as diagnostic characters for species identification.