Annual herb, 1.5–25 cm tall. Roots fibrous, not very extensive. Stem branched at base, with reddish tint, with 4–6 prominent ribs decurrent from the leaf bases; interpetiolar stipules triangular, with abundant papillae on outside. Leaves opposite as well as 4 together higher up on the main branch under the inflorescence, 6–20 mm long, 2–5 mm wide, elliptic to ovate; secondary veins 4–6 pairs, arcuate, inconspicuous below and above, midrib raised below; base acute, with decurrent lamina; margin flat or slightly revolute, entire; apex obtuse; upper side with many short, transparent papilloid hairs, 0.1–0.3 mm long; lower side glabrous; petiole 1–2 mm long. Inflorescence variable, solitary (occasionally multiple), typically a one-sided cyme (rarely a simple cyme/dichasium or a single flower), unbranched, (1-)4–7-flowered, up to 28 mm long, without bracts or with 1–2 tiny bracts subtending flowers; peduncle 7–15 mm. Flowers actinomorphic, perfect, 5- (rarely 6-) merous. Calyx divided almost to base, green, persistent in fruit; lobes triangular, acuminate, 0.8–1.4 mm long, c. 0.3 mm wide, with slightly papillose margins. Corolla sympetalous, tubular, slightly widening towards mouth, 4–8 mm long, 2.5–3.0 mm wide at mouth, white with pink lobes, aestivation valvate with individual corolla lobes plicate in bud, lobes unfolded when open, closing after a short (8-hour) anthesis, later withering and deciduous; lobes triangular, 1.0–1.5 mm long, ca. 1 mm wide, erect, acute, with smooth margin. Stamens epipetalous and adnate to corolla up to middle of the tube, of equal length, included in corolla; filaments flattened; anthers 0.7–0.8 mm long, shallowly sagittate at base, truncate at apex. Ovary bicarpellate, bilocular, ovoid, ca. 0.4 mm tall, with truncate apex; style 3–6 mm long (including stigma), simple, articulated at 0.5–1.00 mm above the ovary, mostly dehiscent in fruit (except the persistent base); stigma simple, papillose, ‘brush-like' at the height of the anthers. Fruit a bilobed capsule, 1.5–2 mm tall, 2–3 mm wide; dehiscing septicidally, loculicidally and circumscissilly, leaving behind on the rachis a persistent, boat-shaped base with pointed tips (‘carpoatlas' in Fernández Casas' (2003) terminology); light brown, warty to papillose; with ca. 0.5 mm tall style remnant. Seeds brown, round, reticulate surface when dry, ca. 0.7–1 mm in diameter.