Global description
Euphorbia peplus is a small annual erect herb, glabrous, reaching up to 50 cm high. The leaves of the stem are simple and alternate, entire, stalked, with oval-rounded lamina. Those of the inflorescence, also simple and entire, are opposite and sessile, smaller, with oval-oblique lamina. The glands of the inflorescence are extended by two filiform appendages. The fruit is a capsule of 3 loculus which each valve has 2 ribs. The seed, a pale gray color, is elongated, with a hexagonal section.
Cotyledons
The cotyledons have an elliptical, elongated to oblong lamina, rounded at two ends, 14 mm long and 3 to 5 mm wide and a petiole of approximately 4 mm long.
First leaves
The first 2 leaves are opposite, the following are alternate. All these leaves are stalked, with oval- rounded leaf blade, slightly indented at the top.
General habit
Small annual erect herb, glabrous, measuring 10 to 50 cm high, often with two stems at the base.
Underground system
The plant has a taproot system.
Stem
The stem, erect, is often branched from the base.
Leaf
The leaves are alternate and simple, thin and scattered, without stipules. The leaves of the stem are oval, obovate or nearly circular, with rounded, obtuse or emarginate apex, with attenuated or rounded base, margin entire. The lamina measures 0.5 to 2.5 mm long and 0.3 to 1.5 mm wide. These leaves end by a long petiole (8 mm maximum). They are pale green in colour. The leaves of the umbel are opposite, sessile to subsessile, with oval-oblique lamina. They are smaller than those of the stem.
Inflorescence
The inflorescence is terminal and forms an umbel composed of 3 dichotomically branched rays one to four times. At the end of the rays is a cyathium consisting of an oval cup, with apiculate end, broad base, with entire margin bordered by four glands in the shape of a crescent with a tapered end.
Flower
The cup includes a few male flowers reduced to a stamen and a female flower reduced to a 3-cell ovary long pedicelled and hanging outside the cup.
Fruit
The fruit is a capsule 3 loculus of 2 mm in diameter, with a smooth envelope. The back of each loculus has a double winged keel.
Seed
The seed (0.5 to 1.4 mm long) is an elongated ovoid, of hexagonal section. It is covered with a longitudinal furrow and bears a caruncle. The faces are hollowed with 3 or 4 small cavity arranged in a line. It is light gray.