Tristemma

Perennial herbs or shrubs, with sharply 4-angular or -winged stems and branches, hairy or bristly. Leaves opposite, longitudinally 5-7-nerved. Flowers 5-merous, sessile or subsessile, in terminal heads surrounded by leaves and leafy bracts; inner bracts coriaceous, chaffy or membranous. Calyx: tube/receptacle ovoid or ovoid-oblong, glabrous or densely setose in upper half or with 1-6 rings of bristles; lobes persistent, +/- reflexed, ciliate at margin; intersepalar segments 0. Petals mauve, pink or blue-violet rarely white. Stamens 10, subequal; anthers lanceolate, all similar, yellow, pedoconnective short with an anterior 2-lobed or 2-fid appendage at base. Ovary 5-locular, adnate to calyx tube/receptacle all around to above middle. Capsule 5-valved, with fleshy placentas, usually splitting irregularly. Seeds many, cochleate.