Sturdy aromatic perennial herb. Stems 30-100 cm, thick, quadrangular, below with multicellular eglandular hairs, above densely glandular-viscid with spreading glandular hairs. Leaves broadly ovate, 6-18 x 5-10 cm, crenateserrate, acute, basally cordate or hastate, eglandular-pilose mainly on venation below and gland-dotted; petiole very long, up to 20 cm on basal leaves. Inflorescence of simple or branched racemes. Verticillasters 4-6-flowered, distant or approximating. Bracts ovate, c. 10 x 5 mm. Pedicels up to 8 mm, spreading erect. Calyx often purple- or violet-coloured, broad obovate-campanulate, 12-15 mm scarcely longer in fruit, densely glandular viscid; upper lip entire or shortly 3-toothed; lower lip bifid; tube glabrous within. Corolla very large, up to 40-50 mm and 15 mm wide at throat, purple, violet or deep blue, rarely white; tube somewhat curved, widening from base, annulate or exannulate within; upper lip c. 10 mm, straight or falcate; lower lip longer than upper. Lower theca smaller than upper one but bearing pol¬len. Nutlets obovoid, dark brown, c. 4 x 3 mm.