Erect, annual herb, 10-25 cm tall. Cauline leaves 4-8 x 2-5 mm, ovate, elliptic, 3-lobed (very rarely 4 lobed) with truncate base; lobes acute-acuminate, longer than broad, upper antrorse, lower patent (4-5 x 2-3 mm, elliptic, lobes acute in aestival and 5.5-8 x 3.5-5 mm, ovate, lobes acuminate in autumnal form). Racemes lax. Floral leaves similar to cauline leaves, mostly ovate, rarely elliptic, 4-8 x 3-6.5 mm (4-5 x 3-4 mm in aestival and 5.5-8 x 4.5-6.5 mm in autumnal form). Flowers 7-10 mm long; pedicels c. 0.5 mm long. Calyx 3-6 mm long; lobes 2-2.5 x 0.5 mm, equal; tube 3-5 mm long. Corolla white with yellow throat, dorsally 6.5-10 mm long; tube 3-5 mm long. Upper lip 3-5 mm long, externally pubescent. Lower lip 3-5.5 mm long; lobes oblong or obovate, obcordate, erose-slightly notched, middle lobe largest 2-4 x 1-3 mm, left and right lobes 1.5-3 x 1-2.5 mm equal or subequal. Two anthers with equal and two with unequal awns; hairs short, equalling the shorter awn. Capsule 4.5-6.5 x 1-2.5 mm (c. 4.5 x 1 mm in aestival and 5-6.5 x 1.5-2.5 mm in autumnal form), oblong, retuse-slightly emarginated, ciliate at the upper end; cilia soft. Seeds 6 per capsule, oblong, obtuse.