Comparative wood anatomy of Astropanax and Neocussonia, an Afro-Malagasy lineage of Araliaceae

Astropanax and Neocussonia are two recently resurrected genera of Araliaceae that had long been considered as an Afro-Malagasy lineage of Schefflera. The wood structure of 11 Neocussonia spp. and eight Astropanax spp. has been studied. Neocussonia shows a higher average length of vessel elements (1319 μm) and number of bars on perforation plates (up to 66) than any other Araliaceae examined to date. Neocussonia is distinct from Astropanax by its smaller diameter and higher frequency of vessels, rare occurrence of simple perforation plates, more numerous bars on scalariform perforation plates and smaller intervessel pits. The interspecific variation in percentage of simple perforation plates, bar number on scalariform perforation plates, vessel frequency and uniseriate ray number is affected by seasonality in temperature and precipitation. The sharp distinction in wood structure between samples of A. abyssinicus from Cameroon and Burundi suggests that the populations from different parts of the disjunct range represent two different species. Our data also suggest that A. goetzenii is an artificial group. Astropanax myrianthus from Madagascar and A. polysciadus from continental Africa, two cryptic species that have long been included in Schefflera myriantha, show significant differences in vessel size and grouping, percentage of simple perforation plates and intervessel pit size.