Annual or perennial, erect, hispid herb, up to 1 m high; stem stout, nodes thickened with axillary whorls of hispid, yellow, 1.5-3 cm long, straight, stout spines; leaves subsessile in whorls of 6, oblong or linear-lanceolate, tapering towards both ends, acute apex, entire margins, sparsely hispid with long, white hairs; flowers subsessile, forming a dense cluster in leaf axils; bracts linear-lanceolate; bracteoles narrow, small; calyx 4 partite, sepals lanceolate, upper rather the largest, acute, lower obtuse, emarginate or shortly bifid, hairy; corolla blue-purple with yellow throat, glabrous, tube oblong, straight, abruptly widening, bilipped, subequally 5-lobed; stamens 4, didynamous, adnate at the throat, exserted, filaments glabrous, anther cells-2, equal, oblong, muticous; ovary 2-celled, ovules 1-2 in each locule; style pubescent; stigma linear; capsule linear-oblong, shorter than calyx, glabrous, 4-8 seeded; seeds minute, hairy.