The genus Lophopyxis Hook. f. (Lophopyxidaceae)

When revising the Icacinaceae from SE. Asia and Malesia recently, my interest was drawn again to the genus Lophopyxis Hook. f. Designated by its author (1887) tentatively as a member of the Euphorbiaceae, it was rejected from this family by Pax as early as 1890. Engler (1893) transferred Lophopyxis to the Icacinaceae as the type of a new subfamily Lophopyxidoideae. Hallier f. (1910) disputed Engler’s view and retained it in the Euphorbiaceae, from which it was excluded again by Pax & Hoffmann in 1931. A possible place in the Rhamnaceae and Flacourtiaceae was considered and rejected by Gilg in 1918; Bakhuizen van den Brink Jr. & van Steenis (1966) likewise rejected the former, though its alliance with the Rhamnaceae was firmly expressed by Airy Shaw (1966). Other authors, as Pierre quoted by Boerlage (1890), inserted Lophopyxis in the Saxifragaceae, Schumann (1898) in the Olacaceae, and Ridley (1922) in Bentham’s Olacineae. In more recent times the genus was referred again to the Icacinaceae by Schellenberg (1923) and Kanehira (1931), but excluded from that family by Hallier f. (1921) and Sleumer (1942). Dahl (1955), discussing the pollen morphology of Lophopyxis, stated that the range of pollen forms known to exist within the Euphorbiaceae could include that of Lophopyxis. Erdtman in the newest edition of his ‘Pollen Morphology and Plant Taxonomy’ (1966) still placed it under Euphorbiaceae. Hutchinson (1959), and subsequently Scholz (1964), place it in the Celastraceae. Though Lophopyxis fits in the general circumscription of the Celastraceae, and shares the winged fruit with the subfamily Tripterygioideae, it cannot be placed in the latter, which all have basal ovules, whilst Lophopyxis has pendent (and certainly epitropous) ones. If placed in the Celastraceae, it would keep an isolated position, as, for instance, does Siphonodon. There is thus no certainty as to the right place of this genus, whose gross morphology, wood anatomy, embryology, and pollen morphology is so well known to-day, in one of the established plant families. It therefore seems justified to regard it as the type of a family of its own within the Geraniales-Sapindales-Celastrales. Suggested already by van Tieghem (1897) and Pierre (1897) casually as Lophopyxidacées’, the family was formally described by Pfeiffer (1951) who raised Engler’s Lophopyxidoideae to family rank, and recently conceived by Airy Shaw (1966).