A sprawling annual (to short-lived perennial) with weak branching stems that are usually decumbent at the base, ascending distally to around , often supported by other plants. The stems are cylindrical and glabrous except for a single line of hairs that runs lengthways, changing sides at each node. Other parts of the plant are usually entirely glabrous. The leaves are arranged in opposite pairs, the lower ones having long (2−5 cm), narrowly winged
stalks and a broadly oval-triangular blade about 3 cm long by 1.5 cm wide. The upper leaves are
sessile or only very shortly petiolate, slightly larger and more oval. The leaves have one strong central vein along the midrib and about 5 lateral veins on each side. The flowers are borne singly in the uppermost leaf axils on slender 2−3 cm stalks, initially spreading and reflexed, later erect. Each flower has five sepals, 5−6.5 mm long, lanceolate, glabrous or rarely pubescent, with an acute apex. There are also five white petals which are divided almost to the base, giving the impression that there are ten. The petals are usually about the same length as the sepals or just slightly shorter, the whole flower being about 10 mm in diameter. There are 8−10 stamens with reddish anthers, and three styles. It flowers between April and July in Northern Europe. The stems can remain alive and produce tillers which overwinter and flower the following year. Seeds are
tuberculate, dark reddish-brown, 1.3−1.7 mm in diameter. The tubercles are conical, with an acute apex. ==Taxonomy==