Annual herb, up to 60 cm high, unbranched (sometimes with branched inflorescence). Stems and branches up to 0.3 cm in diam., terete to quadrangular, narrowly 4-winged; internodes 1-6.8 cm long. Leaves sessile, evenly arranged along stem; blade membranaceous, linear, rarely ovate (lower leaves more ovate), (0.3-)1-2.5(-3.3) x 0.1-0.3 cm, margin flat, apex acute, base attenuate. Inflorescence 1-10-flowered; bracts and bracteoles awl-shaped, 1-3 x 0.5-1 mm; pedicel 1.5-2.5 mm long. Flowers erect to horizontal (rarely nodding); calyx pale green to green, 2-6 x 3-4 mm, lobes narrowly triangular to triangular, often flaring, 1.5-5 x 1-2 mm, margin slightly hyaline, apex acute; corolla white, light to dark blue, light rose to mauve to dark purple or brownish, base whitish, inside of tube white or blue/white-striped in some blue flowers, funnel-shaped, (5-)11-15(-25) mm long, 3-7 mm wide at mouth, lobes triangular to narrowly triangular, rarely ovate to narrowly ovate, 2-10 x 1-2.5 mm, apex acute; stamens not exserted from corolla mouth, filaments 4.5-8(-12) mm long, straight or slightly bent anthers white, sometimes turning yellow-brown, oblong, 0.5-3.3 mm long, straight (?) after anthesis; pollen exine reticulate with large spine-like processes; pistil 5-21 mm long, ovary 1-5 x 0.8-3 mm, style 2-11 mm long, stigma lobe linear (less often ovate), 1.5-4.5 mm. Fruit erect to nodding, green to brown, ovoid, 3-9 x 2-5 mm; seeds brown, 0.3-0.4 mm in diam.
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