Siolmatra Baill.
Siolmatra Baill., Bull. Mens. Soc. Linn. Paris 1: 458. 1885.
Type: Siolmatra brasiliensis (Cogn.) Baill.; basionym: Alsomitra brasiliensis Cogn., St. Hiliare s.n. (P). Brazil.

Perennial climber with several meters long woody shoots and dioecious sex system. The leaves are compound, petiolate, the petiole with a basal ring-shaped callus, the blade is 3-palmate or 5-pedate, the lateral leaflets are asymmetric. The tendrils are apically bifid, coiling above and below the branching point. The flowers are produced in panicles. The receptacle-tube is saucer-shaped with three small sepals. The corolla is contorted with five unguiculate, obovate, whitish petals. The five stamens are inserted at the base of the tube on short, free filaments. The anthers are all monothecous with straight, horizontal thecae containing tricolporate, striate, and small pollen (polar axis 24-28 µm, equatorial axis 23-26 µm, (Khunwasi 1998)). The ovary is obconical, subtrigonous, trilocular at the apex and unilocular at the base. The three placentae contain two pendent ovules. The three styles end in bilobed, reniform stigmata. The fruit is a nodding, obconical-subtrigonous capsule with truncate apex, up to 3 cm long, dehiscent by a triradiate, apical split. The seeds are strongly compressed, ellipsoid with yellowish brown, finely verrucous testa, the margin with c. 2 cm long, membranous wing along the chalaza-micropyle axis.

The two species grow in tropical rainforest of the Amazon basin (Brazil, Peru, Bolivia).

The genus Siolmatra is placed in tribe Zanonieae, where it is sister to the Asian genus Zanonia, from which it split about 24 million years ago (Schaefer et al. 2009, Schaefer & Renner 2011).