Systematic implications of wood and bark anatomy in the Pacific Island genus Meryta (Araliaceae)

Wood anatomy was examined in 16 species of Meryta (a genus of c. 35 species) and bark anatomy was studied in 12 species. All but two of these taxa form an assemblage corresponding to the Northern Arc clade, one of two major groups identified by a recent molecular phylogenetic study. M. sinclairii and M. tenuifolia (corresponding to the New Zealand/Fiji clade) differ distinctly by having more numerous simple perforation plates, multiseriate rays with few marginal rows, and the absence of sclerified cells in collapsed secondary phloem, a bark feature that has not yet been found elsewhere in Araliaceae. The increase in abundance of simple perforation plates in the wood of these two species is not accompanied by a decrease in the number of bars on scalariform perforation plates. The wood structure of Meryta bears a strong resemblance to members of the Pacific Schefflera clade, sharing similar ranges of variation of several features. Bark characters, such as the diameter of the cortical secretory canals, the types of crystal in cortical cells, the types of axial parenchyma cell in collapsed secondary phloem, and the presence of sheath cells by phloem rays, appear to be of diagnostic value for some species of Meryta.