Small to medium-sized annuals; rhizome absent. Leaves basal and cauline, ±flat, canaliculate or semiterete; dorsal epidermal cells dilated; ventral epidermal cells ±enlarged; usually with marginal sclerenchyma. Inflorescence terminal, cymose; flowers usually subsessile, borne singly or in few-flowered, mostly distal loose clusters; floral bracteoles present. Stamens 6, rarely 3. Seed without distinct outer seed coat, small; appendages absent.