Woody vines; stipules interpetiolar, distinct, mostly enlarged to resemble miniature leaves, persistent or eventually deciduous; leaves decussate; petiole eglandular or often bearing small glands near apex; lamina eglandular or bearing tiny glands against abaxial midrib near base. Inflorescence an elongated axillary pseudoraceme of 10–20 flowers; bracts and bracteoles present but very small, eglandular, ± persistent; pedicels short-pedunculate. Flowers radially symmetrical, the only flowers known morphologically bisexual but probably functionally pistillate and the species dioecious (see discussion below). Sepals eglandular, leaving petals exposed in enlarging bud; petals white, glabrous, spreading in anthesis, with a short claw, the limb flat or (generally) concave, ovate or broadly elliptical, entire or somewhat erose or denticulate near the base; stamens 10, glabrous, the filaments short-connate only at base, longer opposite petals than opposite sepals; anthers opening longitudinally, basifixed, the locules separated on a wide flat connective; gynoecium 3-carpellate; ovary 3-locular, each locule containing 1 ovule; styles 3, distinct, of uniform thickness their whole length, arcuate-ascending, the stigma large, sagittate to reniform, stigmatic over the whole upper surface. Fruit dry, breaking apart at maturity into 3 samaras borne on a short pyramidal torus; samara with the dominant lateral wing elliptical, entire or undulate at margin, the dorsal wing much smaller, elliptical, folded over on itself and appressed to nut, the margin notched and undulate; torus subtended by a fleshy 3-lobed disc becoming evident after fall of samaras. Chromosome number unknown.
Madagasikaria resembles its sister-genera, Rhynchophora and Microsteira, in its radially symmetrical flowers with white, nearly entire petals. The flowers of the only known collection of Madagasikaria are morphologically bisexual, but the pollen is inaperturate, which led Davis (2002) to suggest that those flowers are probably functionally pistillate, as in the two sister genera; when a collection is found with staminate flowers they will probably lack a gynoecium, as is the case in Rhynchophora and Microsteira (W. Anderson, 2001b [pdf]), making this genus functionally dioecious like the other two.
Madagasikaria is notable among Malagasy Malpighiaceae in its leaflike stipules and schizocarpic fruit breaking apart into large elliptical samaras bearing a peculiar dorsal wing folded over on itself. Similar stipules and elliptical samaras (but not with a folded dorsal wing) are found in some species of the African genus Triaspis, but the morphological differences discussed by Davis (2002) and the phylogenetic placement of Madagasikaria and Triaspis in our tree for the Malpighia clade all argue for the recognition of Madagasikaria at the level of genus.
Reference: C. Davis, 2002.
Photos: M. andersonii
Drawing: M. andersonii