Oncosiphon

Glabrous or pubescent annual herbs. Leaves alternate, variously pinnatisect. Capitula radiate or discoid, solitary or in corymbs, pedunculate. Involucre subglobose; bracts in several rows, apically obtuse or acute, with scarious margins, with or without central resin canal. Receptacle flat, convex or conical-globose, epaleate. Rayflorets, if present, female, fertile, strap-shaped; corolla white. Discflorets bisexual; corolla always 4-lobed; lobes often cucullate; tube conspicuously swollen and of thick and brittle texture; limb campanulate and partly enervate. Anthers ecalcarate and ecaudate. Style branches with or without central resin canal. Cypselas yellowish brown, +/- terete but tapering at base, 4-ribbed, with abaxial entire or toothed rim, glandular between ribs especially on adaxial side; pericarp very thin; epicarpic cells +/- sclerenchymatous, elongated with narrow lumina; testa epidermis cells with thick, sinuate walls. Pappus 0. x = 9 (aneuploids, B-chromosomes).