Survey of the bark anatomy of Araliaceae and related taxa

Kotina, Ekaterina; Oskolski, Alexei A.


The bark structure in 61 species, belonging to 17 genera of Araliaceae, 2 genera of Myodocarpaceae and 2 genera Apiaceae (subfam. Mackinlayoideae) were examined. All of the taxa under study share the presence of: secretory canals in the cortex and secondary phloem, two types of axial parenchyma (sheath parenchyma surrounding secretory canals and phloem parenchyma accompanying sieve tubes), and the absence of fibres in the secondary phloem; these features can be regarded as synapomorphic for the suborder Apiineae Plunkett & Lowry, the core group of Apiales. Myodocarpaceae are distinguished by their homogeneous secondary phloem rays, whereas the hallmark of Mackinlayoideae is the thickened tangential walls of their phellem cells. The occurrence of styloids in the parenchyma cells of Myodocarpaceae points to a relationship between this family and Pittosporaceae, where this feature is common (Metcalfe & Chalk 1950). Some features of the secondary phloem probably reflect the ancestral condition for Araliaceae, such as: the occurrence of prismatic crystals in cells of axial parenchyma and rays, the sclerification of axial parenchyma, and the radial type of dilatation. Most members of the Asian Palmate group share the phellem cells with thickened walls, the occurrence of druses and sclereids in the axial parenchyma. The Polyscias s. lato subgroup can be distinguished by radial dilatation of the secondary phloem. Bark anatomical data confirm the isolated position of the sect. Schefflera clade within Schefflera and, therefore, the polyphyly of this genus. The length of sieve tube members shows no steady trend in its evolution within the Araliaceae and related plant groups. The sieve tube members are commonly shorter than the vessel elements in wood from the same plant samples. The rays in non-collapsed secondary phloem are commonly of the same structure as the secondary xylem rays in the corresponding species. There is no correlation, however, between the occurrence of radial secretory canals in secondary phloem and in wood. The spines in Araliaceae can be derived either from the cortical parenchyma, or from the periderm; their origin should be taken into consideration by use of this characteristic in taxonomy. Schefflera selloi has a remarkable feature: schizogenous secretory cavities occurring in the phellem. This uncommon feature has not yet been reported in Araliaceae and related taxa. The presence of idioblasts in the cortical parenchyma is restricted to the temperate species, whereas sclerified periderm cells, prismatic crystals in the axial phloem parenchyma and radial secretory canals were found exclusively in the tropical and subtropical taxa.


bark anatomyaraliaceaemyodocarpaceaemackinlayoideaeapiaceae