Flower:

Flowers are tiny and nearly indistinct, 1 to a few clustered in leaf axils along the branches. 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 pink, barely discernible petal-like appendages with a thickened gland at the base that is green to red. The male flower anthers are white to yellow and nearly indistinct. The single female flower in the center is green, the small pistils 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, narrowly oval to oblong, ¼ to 6/10 inch long, surfaces hairless and solid green, typically shallowly toothed especially on the rounded tip, strongly asymmetrical, on a short stalk, with a bit of fringe at the leaf nodes. Stems are hairless, branching heavily from the base and upper branches, forming dense spreading mats up to 12 inches across, or somewhat open and ascending in surrounding grasses. Leaves and stems exude milky sap when broken.

Fruit:

Fruit is a sharply 3-sided, stalked capsule, nearly pyramidal in shape, up to 2 mm long and wide, that develops rapidly from the center of the cyathium, initially hanging down, becoming erect at maturity.

Seeds are less than 1.5 mm long, light brown with a white coating that rubs off, 4-sided in cross-section, oval-oblong in outline, covered in tiny pits across the surface, and with conspicuous transverse ridges.

Notes:

Ridge-seed Spurge, formerly Chamaesyce glyptosperma, is probably the most common and widespread mat forming spurge species in the Midwest and is widely adapted to harsh urban environments, being weedy in compacted lawn areas and cracks of hard pavement. In the metro and southeast counties it frequently shares these habitats with Spotted Spurge (Euphorbia maculata). Characteristics that identify Ridge-seed Spurge from others are the hairless stems, leaves that are not red-spotted and mostly oblong with fine teeth at least on the tip end, and angular seeds with conspicuous transverse ridges. Minnesota has two other hairless, mat-forming Spurges, both of which lack transverse ridges on the seeds: Geyer's Spurge (Euphorbia geyeri), which has toothless leaves, and Thyme-leaved Spurge (Euphorbia serpillifolia), which has leaves usually broadest above the middle and often have a red splotch in the center. The other two mat-forming Spurges in Minnesota, Spotted Spurge (Euphorbia maculata) and Prostrate Spurge (Euphorbia prostrata) both have hairy stems, leaves and capsules.