Perennial herb (sometimes flowering in seedling stage), taproot becoming very stout and woody, up to c. 20 mm diam. at crown, stems (150-)200-1200 mm tall, up to c. 6 mm in diam., few to many from the crown, simple or laxly branched low down, occasionally almost twiggy, densely glandular-puberulous with few to many long (0.5-1.5 mm) glandular hairs as well, these simple or dendroid, often leafy mainly in the lower part, pedunculoid upwards, but in branching specimens leafy on upper parts. Leaves opposite, bases connate, uppermost often alternate and passing into distant bracts, 15-150 x 2-18 mm, oblanceolate or narrowly elliptic, apex ± acute, base tapered to a petiole-like part, margins subentire to distinctly serrate, both surfaces glandular-puberulous, usually with many, sometimes few, long (c. 0.3-1 mm) simple or dendroid glandular hairs as well. Flowers many in a dense terminal raceme, capitate at first, oblong in fruit and up to c. 150 mm long, sometimes with 1 or 2 subsidiary inflorescences arising some distance below the main one and sometimes overtopping it. Bracts (lowermost) c. 3-10 x 0.5-1 mm, oblong. Pedicels (lowermost) 1.5-4 mm long. Calyx obscurely bilabiate, tube 0.4-1 mm long, anticous lobes 3.6-5.5 x 0.8-1.2 mm, posticous lobes 4-6 x 0.8-1 mm, all enlarging in fruit, densely pubescent all over with both glandular and eglandular hairs, some hairs up to 0.2-1 mm long. Corolla tube 8-10 x 1.3-1.75 mm in throat, cylindric, abruptly expanded in upper half, mouth strongly compressed laterally, limb almost regular, c. 7-13 mm in diam., posticous lobes 3-4 x 3-5.5 mm, anticous lobe 3-5 x 3-5.5 mm, all lobes suborbicular, white with greenish to yellow patches at the bases, or the three anticous lobes wholly yellow, the colour coalescing in the throat and extending down the inflated part of the tube, outside of tube and backs of lobes densely pubescent, hairs up to 0.2-0.75 mm long, glabrous inside except for minute glandular hairs sometimes present below insertion of posticous filaments. Stamens 4, anticous anthers 0.4-0.6 mm long, just included, posticous anthers 1.4-1.6 mm long, deeply included, posticous filaments bearded with clavate hairs. Stigma 0.6-2 mm long, about equalling or somewhat longer than style, deeply included, tip sometimes minutely bifid. Style 0.6-1.5 mm long. Ovary 1.3-2.5 x 1-1.5 mm, elliptic. Capsules 4-6.5 x 2.6-3 mm. Seeds c. 0.7 x 0.2-0.3 mm, violet-blue. Flowering principally between July and September.
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