Woody vines; stipules small, triangular, borne on very base of petiole or on adjacent stem, or absent; leaves opposite, subopposite, or alternate; petiole biglandular at or above middle; lamina eglandular or bearing small glands on margin, the tertiary veins strongly parallel (scalariform). Inflorescence a single short axillary raceme of 3–7 (–9) 4-flowered umbels, with 1 umbel terminal and the other 1–4 pairs axillary to bracts bearing stipules and often petiole glands; floriferous peduncles short or absent; bracteoles small, one of each pair bearing 1 bulging eccentric abaxial gland toward center of umbel, the gland 0.7–1.1 mm long, circular or elliptical in outline; pedicels circinate in bud. Sepals all eglandular or the lateral 4 abaxially biglandular; corolla bilaterally symmetrical, the posterior petal strongly differentiated from the lateral 4; petals bright yellow, glabrous; stamens glabrous; anthers with the connective abaxially broad and swollen; ovary with the carpels nearly distinct; styles inserted low on ventral face of carpels, the anterior style shorter than the posterior styles, the apex with a large internal stigma and dorsally truncate, apiculate, or bearing a hook up to 0.3 mm long. Samaras separating from a short pyramidal torus; samara with a large, membranous, usually subcircular lateral wing borne on upper edge of nut, cleft to nut at apex and continuous at base or occasionally cleft to nut at both apex and base; dorsal wing small; intermediate winglets absent. Chromosome number unknown.
Four species in forests of northern South America. [map]
Excentradenia resembles Hiraea in the scalariform tertiary veins of the leaf, lamina glands borne only on the margin, flowers borne ultimately in umbels, nearly distinct carpels, and a subglobose nut in the samara. Hiraea is distinguished by its elongated stipules borne at least somewhat above the base of the petiole (and often above the middle), inflorescence consisting of an axillary cyme of 3–7 4-flowered umbels or a single umbel of 4–many flowers, eglandular bracteoles, pedicels straight in bud, and lateral wings of the samara cleft to the nut at both apex and base, producing two completely separate wings. The difference between their inflorescence branching deserves further comment. In those specimens of Excentradenia in which there are more than three umbels, they are arranged as two to four successive pairs originating from the same axis, followed by a terminating umbel. In Hiraea this never happens. If the inflorescence is branched, it is strictly cymose—it terminates in an umbel, and the two lateral branches are axillary to a single pair of bracts on the stalk below. Those branches terminate in an umbel, and may be subtended by another pair of lateral branches.
Photos: E. primaeva, E. propinqua
Drawings: E. adenophora, E. primaeva, E. propinqua