Flower:

Flowers are tiny and indistinct, mostly single in the leaf axils, thought may be in small clusters near branch tips. A small cup, 1/8 inch across, holds the male and female flowers in the center.

The rim of the cup has 4 white to pinkish, petal-like appendages with a thickened gland at the base that is green to red. The male flowers have yellow anthers while the single female flower in the center is green, the small styles atop a round, three part ovary on a short stalk that extends out from the flower center. The structure of this flower is called a cyathium and common to all the Euphorbias.

Leaves and stems:

Leaves are opposite, broadly oblong to oval-elliptic, 1/6 to ½ inch long, toothless, hairless, rounded to slightly dented at the tip, often with a minute sharp point, slightly asymmetric at the base, on a short stalk, with a bit of fringing at the leaf nodes. Stems are smooth, branching from the base and upper branches, forming spreading, prostrate mats up to 12 inches across. Leaves and stems exude milky sap when broken.

Fruit:

Fruit is a stalked 3-lobed capsule, generally pyramidal in shape, 1/10 inch wide, that develops rapidly from the center of the cyathium, initially hanging down, becoming erect at maturity, and often a reddish color.

Seeds are 1.1 to 2 mm long, pale gray-brown to nearly white, egg-shaped, nearly round in cross-section, with a distinct dark ridge along one side, and covered in shallow pits that are visible with strong magnification, but appears smooth to the naked eye.

Notes:

Geyer's Spurge is just one of several native and non-native spreading mat type spurges common in Minnesota. Characteristics that identify this from others are the hairless stems, toothless leaves and essentially smooth seeds. Of the two other hairless, mat-forming Spurges in Minnesota, Ridge-seed Spurge (Euphorbia glyptosperma) and Thyme-leaved Spurge (Euphorbia serpillifolia) both have leaves with fine serrations at least at the tip of most leaves, and somewhat smaller seeds that are more angular in cross-section. The other two mat-forming Spurges in Minnesota, Spotted Spurge (Euphorbia maculata) and Prostrate Spurge (Euphorbia prostrata) both have hairy stems, leaves and capsules. Geyer's Spurge is also less broadly weedy than others and typically found only in relatively undisturbed sand prairie habitats.