Annual or perennial juicy herb (5) 10–60 (80) cm. high or more, usually erect; stems simple or little branched, glabrous or pubescent mainly on younger parts. Leaves opposite, rarely in threes, sometimes ± densely crowded on the upper part of the stem, sessile or shortly petiolate; lamina (1·5) 2·5–7 (10) × (0·3) 0·8–2 (3) cm., linear, lanceolate, ovate or elliptic to (rarely) subcircular, the lower ones often much broader than long and shorter than the higher ones, chartaceous or thinly chartaceous, usually glabrous but sometimes pubescent on both surfaces, dark green on the upper, greyish-green or glaucous on the lower surface, apex acute or obtuse, margins slightly crenate-denticulate, base cuneate to rounded or very rarely subcordate; petiole 0·2–0·5 cm. long, pubescent or glabrous. Flowers solitary, very rarely in pairs, axillary, usually white but sometimes white with yellow spots (raised honey guides) inside and a pinkish spur, pink or often with an orange throat; pedicel 2–5 (7) cm. long, glabrous or pubescent; bracts very short, lanceolate-triangular, acute. Lateral sepals 3–5 × 0·7–2 mm., lanceolate to broad-lanceolate (rarely triangular-lanceolate) usually glabrous; posterior sepal broadly and obliquely infundibuliform, 4–10 mm. deep (excluding the spur), up to 1·3 cm. in diam. at the mouth, abruptly constricted into the spur, distally acute; spur 4–10 mm. long, slightly incurved or more rarely straight, usually tapering into a fine point (see t. 26 figs. 2–3). Anterior petal 8–12 × 8–12 mm. (when flattened), dorsally with a slender crest, glabrous or with a row of ± stiff white hairs on the crest; crest terminating in an acute or bluntish point. Lateral pair of united petals 15–20 (25) mm. long, deeply 2-lobed; anterior lobe 9–15 × 6–9 mm., transversely broadly oblique-obovate, rarely obtrapeziform; posterior lobe about 1/2 to 2/3 the size of the anterior one, oblique-obovate to broadly obdeltate (see t. 26 fig. 24). Ovary glabrous. Capsule 0·9–1·5 cm. long, fusiform, glabrous or rarely sparsely hairy when young. Seeds numerous, c. 1·6 mm. in diam., broadly elliptic in outline, laterally slightly flattened, rusty or dark brown, with a densely papillose surface, glabrous.
