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Annual or perennial erect, subprostrate or twining herbs with mostly hairy stems. Leaves paired; stipules with base divided into several narrow segments. Flowers small and white or rather large and coloured, hermaphrodite, monomorphic or dimorphic, in cymose heads, which in fruit develop into a long simple spike with the fruits geminately arranged and a solitary remotely placed flower in the axil at the base of the spike (save in subgen. Volubiles where the cluster remains dense). Calyx-tube ovoid or elongate-oblong; lobes unequal, 5, 1–3 foliaceous and larger than the rest, alternating with small colleters. Corolla-tube long and narrow, with a markedly ovoid-oblong apical dilation in long-styled forms; throat densely hairy; lobes in small-flowered species elliptic, but in large-flowered species broader, ovate to orbicular, narrowing to the base where the lobes are often connate for a short distance. Stamens completely exserted in short-styled forms. Style exserted in long-styled forms, the stigma bifid with filiform lobes; anthers completely included in the apical dilation of the corolla tube. Capsule oblong, compressed, ribbed, opening by apical valves and also frequently splitting longitudinally. Seeds small, reticulate.