Herbs, perennial [annual herbs or shrubs], without cystoliths, anisophyllous. Leaves usually in pseudo-whorls of 4 [or opposite], sessile to subsessile; leaf blade margin entire to dentate. Flowers axillary and solitary or many in terminal dense headlike spikes; bracts often clustered in up to 5 pairs, imbricate, leathery, margin often bristly dentate with bristles barbed; bracteoles absent [or 2]. Calyx included in bracts or ± exserted, 4-lobed; lobes in 2 unequal opposite pairs, thickened-horny at base, posterior and anterior lobes larger and 2-7-veined, lateral pair smaller and 1-veined. Corolla tube shorter than limb, expanded from base and constricted near apex; limb a single (lower) lip; lip elongate, 3[-5]-lobed. Stamens 4, didynamous, inserted at or near apex of corolla tube; filaments bony, with lower pair straight and upper pair curved, broad, flattened, usually bifurcate apically into a branch bearing an anther and a toothlike appendage; anthers 1-thecous; theca bearded. Ovary glabrous, with 2 ovules per locule; style linear; stigma 2-cleft. Capsule not stipitate, oblong to ellipsoid, 2(-4)-seeded; retinacula present. Seeds discoid, covered with long branched hygroscopic trichomes.
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