Duration: Annual
Nativity: Non-Native
Lifeform: Forb/Herb
General: Annual herb, 20-50 cm tall, from a taproot; branches ascending; stems sparsely hairy with gland-like stipules.
Leaves: Mostly opposite but crowded and alternate towards top of plant where they subtend the flowers and become whitened at the bases; blades elliptic to lanceolate, 4-8 cm long, coarsely toothed, with a tapered base and acute tip, lower surface with stiff, strongle tapered hairs. Petioles nearly as long as leaf blades.
Flowers: Has the highly modified flower structure characteristic of Euphorbias. Structures called cyathia appear to be individual flowers, but are composed of fused-together bracts forming a cup or involucre, with peripheral nectary glands which are often subtended by petal-like bracts called petaloid appendages. Within the cup there is a ring of inconspicuous male flowers, each reduced to a single stamen. Out of the middle protrudes a single, stalked female flower which lacks petals. In E. davidii, the cyathia (modified flowers) are clustered into cyme-like inflorescences at branch tips. Involucres are glabrous, bell-shaped, and 2-3 mm high, with 1 (sometimes 2) cup-shaped gland and no petaloid appendages; 10-20 staminate flowers.
Fruits: Capsule 4 mm wide, distinctly 3-lobed, depressed-spheric, glabrous or sparsely hairy, splitting into 3 single seeded sections at maturity; seeds 3 mm long, ovoid, 3-angled, coarsely tubercled.
Ecology: Found in waste places and dry, disturbed sites, below 5,000 ft (1524 m)
Distribution: USDA Plants lists this species as introduced to the US, but USDA GRIN lists it as native to North America, with its native range consisting of KS, NE, OK, TX, WY, CO, NM, AZ, and northern Mexico. It is listed as naturalized in Eurasia, Australia, and the
Notes: E. davidii is often reported as, and was originally placed within E. dentata. These two species are distinguished from other Euphorbia in our area by the combination of being erect annuals with opposite branching; unlobed, dentate leaves 4-8 cm long that are mostly clustered near the top of the plant; and the single cupped gland of the cyathia without any petaloid appendages. Differentiated from E. dentata by the strongly tapered hairs on the undersides of leaves; petioles almost as long as the leaves (vs. 1/3 as long in E. dentata); cyathia with gland-tipped fringes; and angular seeds (seeds are rounded in E. dentata). E. exstipulata is similar but is a smaller plant, under 25 cm tall, and has 4 glands per involucre, and 4 white petaloid appendages. E. davidii, E. dentata, and E. exstipulata are all members of the Pointsettia section of Euphorbia.
Ethnobotany: Unknown, but other species in the genus had medicinal uses.
Etymology: Euphorbia is named for Euphorbus, Greek physician of Juba II, King of Mauretania, while davidii is named for David Lee Anderson 1938- , range management ecologist who spent years in Argentina.
Synonyms: Euphorbia dentata (auct. non Michx.), E. dentata var. gracillima, E. dentata var lancifolia, Poinsettia davidii, Poinsettia dentata var. gracillima
Editor: FSCoburn 2014, AHazelton 2015, AHazelton 2017
