Woody vines; stipules very small, triangular, borne on stem beside base of petiole; leaves opposite; petiole usually biglandular above middle, the glands when present protuberant, usually large and knoblike; lamina eglandular or bearing very small marginal glands, often drawn out into vascularized cilia, on distal half, especially near apex, the tertiary veins weakly or not scalariform. Inflorescence an open, elongated, axillary or terminal panicle or pseudoraceme with the flowers borne singly or (most often) in 2s, 3s, or 4s; floriferous peduncles well developed; bracteoles borne at apex of peduncle, one of each pair bearing 1 bulging eccentric abaxial gland; pedicels slightly circinate in bud. Sepals all or the lateral 4 abaxially biglandular; corolla bilaterally symmetrical, the posterior petal long-fimbriate and strongly differentiated from the lateral 4; petals bright yellow or the posterior yellow and red, glabrous; stamens glabrous; filaments longer opposite sepals, shorter opposite petals; anthers mostly larger on longer filaments, the connective abaxially broad and swollen; ovary with the carpels nearly distinct; styles inserted low on ventral face of carpels, ± bowed or lyrate, the anterior mostly shorter and less strongly bent than the posterior 2, the apex with a large internal stigma and dorsally truncate, apiculate, or bearing a hook up to 0.5 mm long. Samaras separating from a short pyramidal torus; samara orbicular to butterfly-shaped with the lateral wings membranous or chartaceous, cleft to nut at apex and base, borne on upper edge of nut (lateral wings rudimentary and the small dorsal wing dominant in A. mirabilis); dorsal wing smaller and distinct from lateral wings at both apex and base; intermediate winglets absent. Chromosome number unknown.
Four species in wet evergreen or semideciduous forests of Jamaica, southeastern Mexico, Central America, and western South America, sometimes near rivers. [map] — Regional key to genera: Caribbean, Central America.
In several characters Adelphia resembles Excentradenia, most notably the large eccentric bracteole glands, the circinate flower buds, and the samaras with large membranous lateral wings. It is distinguished by its open elongated inflorescence, which is dramatically different from the compact axillary raceme of 4-flowered umbels found in Excentradenia.
Reference: W. R. Anderson (2006b, pp. 170–173), partial revision: description of genus, key to species, nomenclature of species but no descriptions of species (Adelphia only: pdf; entire paper: pdf); unpublished notes on species of Adelphia.