The size of the plant and the number of flowers as well as their size varies considerably according to environmental conditions. In addition some local variation can be observed in the colouration of the petals, which may vary from pure yellow to more or less orange around the throat and in the floral tube. The spreading lobes are rarely completely orange but even within a single population considerable variation is often found.
Annual, with erect, wiry, sparsely branched stem, 10-150 mm tall. Leaves sessile, obovate to linear, dorsiventrally flattened and slightly fleshy, 5-12 x 1-6 mm. Flowers usually in a loose, terminal cluster, funnel-shaped, petals 8-12 mm long, yellow to orange, often darker in tube.
Annual with wiry stems to 20 cm. Leaves opposite, subterete to obovate. Flowers in a terminal thyrse, cup-shaped, yellow to orange, often marked red in throat, petals 8-15 mm long, stigmas terminal on slender styles.
Annuals with erect wiry stems 0.05-0.15 (-0.25) m long, usually sparsely branched. Leaves obovate, elliptic to linear or rarely lanceolate, 5-12 (-18) x 1-6(-10) mm, acute or obtuse, dorsiventrally compressed and often somewhat cymbiform, slightly fleshy, green. Inflorescence usually with one terminal thyrse. Calyx: lobes elliptic-lanceolate, 4-6 mm long, obtuse and with more or less recurved apices, glabrous, fleshy, green. Corolla funnel-shaped, fused at base 2.5-4 mm long, yellow to orange and often marked in a deeper colour in throat of tube; lobes ovate, lanceolate to elliptic, (7-)8-12(-20) mm long, obtuse to acute, without dorsal appendage, recurved. Stamens with yellow anthers. Squamae narrowly oblong, 0.6-1.3 x 0.1-0.3 mm, truncate or slightly rounded, scarcely constricted downwards, fleshy, yellow. Style slender with terminal stigma.