Herb, up to 60 cm tall. Branches somewhat quadrangular. Leaves sessile, opposite, rarely verticillate; blade linear, narrowly elliptic, narrowly obovate, or narrowly ovate, 0.2-2 x 0.05-0.3 cm, apex acute or obtuse, base broadly cuneate, venation hardly visible, 1-3-veined from base; lowest pair of leaves hardly aberrant in shape. Inflorescence loose, simple or repeatedly branched, 1-many-flowered dichasium, 1-10 cm long, bracts and bracteoles linear, 1-4 mm long (basal bracts often leaf-like); pedicels 0.5-6 mm long. Flowers heterostylous (short-, equal-and long-styled); calyx green, weakly winged, 3-8 mm long, lobes linear-lanceolate, apex acuminate, margin sometimes slightly denticulate, scarious; corolla white, pink, or violet, often yellow in throat, tube infundibuliform, 4-9 mm long, inside pilose in middle part, lobes ovate to orbicular, 1.5-7 mm long, apex acute or obtuse; filaments 0.4-1.6 mm long, anthers oblongoid, 0.6-1.5 mm long, connective prolonged above thecae, obtuse to apiculate; pistil 3-7 mm long, ovary narrowly ovoid, stigma oblongoid, 0.6-1.8 mm long, 2-lobed or lobes coherent, papillose. Fruit narrowly ovoid, 5-11 mm long, including persistent style-stigma; seeds globose to conical, irregular, 0.1 mm.
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