Height: 20–80 cm (8–32 in.). Stem branching, with swollen joints, 4-edged, often with purple base, joints and edges, rough-haired mainly along edges, lacking glandular hairs.
Flower: Corolla irregular (zygomorphic), pale yellow, occasionally white or reddish, 20–35 mm (0.8–1.4 in.) long, fused, bilabiate, long-tubed, hairy. Upper lip convex; lower lip 3-lobed, central lobe purple, base with 2 glands. Calyx campanulate (bell-shaped), 5-lobed, lobes rigid, sharp-pointed. Stamens 4, of which 2 short and 2 long. Gynoecium composed of 2 fused carpels. Inflorescence lower part with long gaps, upper part denser, spike-like group formed of dense axillary whorls terminating stems and branches
Leaves: Opposite, stalked. Blade ovate, sharp-tipped, feather-veined, smoothly haired, margin with large, sharp teeth. Inflorescence’s subtending bracts like stem leaves.