Flower:

Flowers are tiny and indistinct in dense clusters at tips of stems and branches. A small cup, 1/8 inch across, holds the male and female flowers in the center. There are no visible petal appendages, rather finely fringed lobe margins with typically 1 to several olive colored glands. The male flower anthers are creamy white to yellow, the single female flower in the center is green, the clump of styles atop a round, three part ovary on a short stalk that extends out from the flower center. The leafy bracts surrounding the cluster are typically white at the base, giving the cluster a soft glow. The structure of this flower is called a cyathium and common to all the Euphorbias.

Leaves and stems:

Leaves are opposite except the lowest leaves which are alternate, ½ to 3½ inches long, narrowly lance-elliptic to egg-shaped, tapered to a slender stalk. Edges are mostly coarsely toothed, occasionally smooth, often a bit wavy.

Leaves are green, often spattered with red spots. Surfaces are softly hairy (pubescent) or with scattered spreading hairs that are denser on the underside. Stems are finely hairy above to wooly towards the base, erect with spreading branches, green to reddish.  Leaves and stems exude milky sap when broken.

Fruit:

Fruit is a three lobed, stalked capsule, 1/5 inch wide, that develops rapidly from the center of the cyathium, initially hanging down, becoming erect at maturity. Seed is light gray-brown, four angled, egg-shaped with tubercule-like projections.

Notes:

Toothed spurge (formerly known as Poinsettia dentata) is highly variable, often related to growing conditions, being more robust on moister sites. While both the Bell herbarium and the DNR list it as native to Minnesota (as both historical and distribution records suggest), some references would question its native North American range and both the USDA and BONAP list it as not even present in the state, but list an apparently similar looking non-native, Euphorbia davidii, present in MN instead. The difference seems to be stiff hairs on E. davidii vs. soft hairs on E. dentata (in either case we'll go with the Bell and DNR on this one). Regardless, it its relatively frequent in metro lanscape margins and waste places and easily identifiable, its structure is strongly reminiscent of the holiday poinsettia to which it is closely related.