Meetings of the Royal Botanical Society of the Netherlands

Fruit and seed structure, vegetative anatomy and pollen morphology of Hua and Afrostyrax have been studied in order to elucidate the taxonomic affinities of these enigmatic genera from tropical West Africa. Hua was initially described in the Sterculiaceae and Afrostyrax in the Styracaceae. Various authors have since then put forward a number of suggestions about the taxonomic affinities, including presence or absence of mutual relationships between the genera and affinities to the Sterculiaceae, Styracaceae, Linaceae s.l., Dipterocarpaceae, Tiliaceae, or Erythroxylaceae. Micromorphological characters strongly support the mutual affinities of the two genera. The common characters are: Fruit wall with outer and inner parenchymatous layers separated by a layer of stone cells. Outer testa parenchymatous, supplied with vascular bundles. Inner testa with an outer sclerenchymatous palisade layer, arising from the outer epidermis of the inner integument. Pollen triporate and operculate. Stomata paracytic. Petiole supplied with cylindrical vascular system enclosing medullary bundle(s). Venation pattern of regularly arranged veinlets enclosing rectangular areolae. Extrafloral nectaries with palisadelike epidermis mostly present. Cristarque cells present in ground tissue of petiole and stem. Node 3-trace, 3-lacunar. Bark enclosed by solid perivascular sclerenchyma ring, traversed by narrow and broad, triangular rays. Wood composed of vessels with simple perforations and alternate wall pitting, libriform fibres, banded paratracheal parenchyma and heterogeneous broad and narrow rays. This complex of characters excludes Styracaceae, Erythroxylaceae, Dipterocarpaceae, Tiliaceae, and Linaceae as close relatives of Hua and Afrostyrax. Out of 50 families studied in the comparisons Sterculiaceae and Bombacaceae appear to show most resemblance in anatomical features, but are sufficiently different in e.g. their possession of mucilage cells or cavities, stratified phloem and more advanced xylem to justify family status for Huaceae, including both Hua and Afrostyrax. The inclusion of Huaceae in Malvales seems justified as was suggested by of a number of previous authors. A full account of the anatomy and a discussion of the affinities of Huaceae has been published in Blumea 20(1), 1972.