Lianas climbing, woody, laticiferous. Branches and branchlets densely stellate hairy. Leaves opposite, simple, pinnately veined; stipules 2, free, minute. Inflorescence axillary, paniculate, multi-flowered, densely stellate hairy. Flowers bisexual, small. Calyx (2-)4(or 5)-partite, segments unequal in length. Petals 3, rarely 4, sepal-like, reflexed. Stamens numerous; filaments free; anthers 4-celled but becoming 2-celled at dehiscence. Ovary 3-loculed, sessile, superior, densely tomentose; ovules 2 per locule; style 1, subulate; stigma minutely 3-lobed. Fruit a capsule, not fleshy, dehiscent but finally septicidal with 3 apical spatulate wings. Seeds unknown.
One species: S China, Myanmar, Thailand.
Baas et al. (Grana 18: 69-89. 1979) provided two interpretations of the perianth, one similar to the above (although with petals (3 or)4(or 5)) and another in which the inner whorl is regarded as a calyx, the outer whorl as bracteoles or an epicalyx, and the corolla consequently absent.
In their detailed review, Baas et al. (loc. cit.) were unable to place Plagiopteron with any confidence and concluded that the genus deserved family rank, following Airy Shaw’s earlier concept (Kew Bull. 18: 249-273. 1965). The molecular evidence presented in abstract by Simmons et al. (Amer. J. Bot. 87(6, Abstracts): 156-157. 2000) placed Plagiopteron clearly in the Celastraceae, close to the Hippocrateoid genera. Savolainen et al. (Kew Bull. 55: 257-306. 2000) and Soltis et al. (Bot. J. Linn. Soc. 133: 381-461. 2000) similarly placed the genus. The general appearance of the plant, a woody climber with fairly large opposite leaves, small flowers in many-flowered terminal cymes, and fruit with Acer-like wings supports this affinity. Further similarities were found in the elastic material of the leaf midrib vascular cylinder. The pollen of Plagiopteron is apparently unusual for Celastraceae (Baas et al., loc. cit.).
Chang Hung-ta. 1989. Plagiopteron. In: Chang Hung-ta, ed., Fl. Reipubl. Popularis Sin. 49(1): 48-50.