Limnophila

Aquatic or marsh herbs, annual or perennial; aerial stems simple to much branched, glabrous or sometimes hirsute, often with pellucid dots and aromatic; submerged stems much branched, glabrous. Leaves: aerial ones opposite or verticillate, sessile, entire to serrate, laciniate or pinnately divided, punctate; submerged leaves laciniate, pinnatifid to capillary-multifid, glabrous. Flowers solitary and axillary, or in a dense, terminal raceme, sessile or pedicellate, bracteate; bracteoles 0 or 2. Calyx tubular, 5-lobed mostly to +/- halfway, rarely shorter; lobes broadly ovate to lanceolate, sometimes acuminate, imbricate, subequal or posterior lobes larger. Corolla tubular, bilabiate, 5-lobed; tube cylindrical or funnel-shaped, glabrous or sparsely hirsute outside, sometimes villous or papillate inside; posterior lip entire or 2-lobed, outside in bud; anterior lip 3-lobed; lobes elliptical or ovate, slightly or much shorter than tube, erect or spreading. Stamens 4 (sometimes 2 in cleistogamous flowers), didynamous, included, posterior pair shorter; filaments linear, arising in corolla tube; anthers bithecate, free, sometimes contiguous at anthesis; thecae separate, usually shortly stalked; staminodes 0. Ovary bilocular, ovoid, glabrous; ovules many; style filiform, bent at right angles at apex; stigma bilamellate. Fruit an ovoid or ellipsoid, septicidal and loculicidal capsule, with 2, often bifid valves. Seeds small, many, ellipsoid; testa thin, dark-coloured. x = 17 (9, 15) (polyploidy).