Woody vine, the stems developing large punctiform lenticels in age; stipules narrowly triangular, distinct, interpetiolar, soon deciduous; leaves decussate; petiole eglandular; lamina mostly soon glabrate on both sides, usually bearing 1–several small glands immersed in abaxial surface in a row set in from margin. Inflorescences axillary, paniculate, open, the flowers in few-flowered pseudoracemes, often with several in a terminal umbel; peduncle and pedicel both developed, the bracteoles borne at or below apex of peduncle; bracts and bracteoles eglandular, caducous or deciduous during enlargement of fruit. Flowers radially symmetrical in all their whorls; sepals imbricate, completely concealing petals during enlargement of bud, nearly distinct, strongly reflexed in anthesis, sericeous on both sides, all eglandular; petals white, obovate, clawed, glabrous, caducous; stamens 10; filaments long and slender, ± alike, nearly distinct; anthers all alike, sparsely pilose or glabrous; receptacle glabrous between androecium and gynoecium; gynoecium comprising 3 carpels connate in the ovary; ovary densely hairy, all 3 locules developed and containing ovules; styles 3, alike, long and slender, with minute terminal stigmas. Fruit indehiscent, dry, hard, woody, ± globose, 2–3 cm in diameter, with 1 locule developed and containing a large seed and the other 2 locules abortive, unwinged or the fertile locule bearing 3 ribs or winglets (2 lateral and 1 dorsal) and the abortive locules unwinged or bearing small partially developed winglets. Chromosome number unknown.
Flabellariopsis was named for its resemblance to Flabellaria, which also has radially symmetrical flowers with long, narrow sepals that completely conceal the petals during enlargement of the bud and are reflexed in anthesis. In both the strongly spreading petals are white and the fruits are indehiscent. Nevertheless, there are differences between them, of which the most significant are summarized in the following key.
|1.||Leaf glands on abaxial surface of lamina (albeit near the margin), the petiole eglandular; lamina soon glabrate on both sides; stipules relatively large, triangular, interpetiolar, caducous; sepals imbricate in bud; petals clawed, caducous; fruit nutlike with the seed-containing locule large, unwinged or bearing ribs or distinct winglets much smaller than nut.||
|1.||Leaf glands on margin of lamina, and often in 2 rows on petiole; lamina adaxially glabrous, abaxially ± persistently sericeous; stipules absent or represented by minute rudiments borne on petiole just above base; sepals valvate in bud; petals spatulate, long-persistent; fruit samaroid with the seed-containing locule small and the lateral wing much larger, membranous, continuous at base.||Flabellaria|
In 1959 [pdf] Wilczek amplified his earlier description of Flabellariopsis by describing and illustrating a large, nutlike fruit with three parallel winglets, two lateral and one dorsal. In the few fruiting specimens available to W. R. Anderson for the preparation of this treatment some specimens show enlarging but immature fruits with winglets like those illustrated by Wilczek, while others with full-sized fruits bear no winglets at all or only ribs where the winglets should be. This difference may prove diagnostic of two distinct species, the one with winglets having a more western distribution and the one without winglets in the east (Kenya and Tanzania), but it is also possible that the variation in nature is continuous; only more fruiting collections will resolve that matter. The winglets, when present, are surely too small to be functional in dispersal, so there may be great variation in a character no longer constrained by selection.
The fruit of Flabellariopsis is probably adapted for dispersal by water, which is not uncommon in New World Malpighiaceae but almost unknown in Old World members of the family (excluding Heteropterys leona and Stigmaphyllon bannisterioides), presumably reflecting the fact that the ancestors of the Old World clades migrated from the New World via wind-dispersed samaras. That brings us to the problem of the ancestry of Flabellariopsis. The latest family phylogeny (Davis & Anderson 2010; pdf) showed Flabellariopsis as sister to the Asian genus Hiptage, with very strong support. Aside from having similar stipules and leaf glands those two genera could hardly be more different in their morphology; see our description of Hiptage. Most striking in Hiptage are the unbranched inflorescences, the bilaterally symmetrical flowers, the short sepals, the hairy petals, the strongly unequal stamens, the single style, and the fruit breaking apart into three samaras, each bearing three elongated lateral wings. If Hiptage and Flabellariopsis did descend from a common ancestor, there have been many significant changes in their morphology as they journeyed to their present distantly separated areas of distribution.
Etymology: The name Flabellariopsis means "resembling Flabellaria." Flabellaria Cav. is another monotypic genus of Malpighiaceae in equatorial Africa.
Drawing: F. acuminata