Duration: Annual

Nativity: Native

Lifeform: Forb/Herb

General: Annual herb, 5-25 cm tall, from a slender taproot; stems erect, spreading, with very slender branches that fork repeatedly; herbage glabrous.

Leaves: Opposite and short-petiolate, located almost entirely at nodes where the stem forks into 2 branches; blades narrowly linear, 1-2 cm long, the margins entire and tightly revolute (curled under), and the midvein impressed on the upper surface of the leaf; stipules narrow and tapering toward the tip, 0.5 mm long.

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 (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. revoluta, the cyathia (flower structures) are mostly solitary in the nodes near branch tips. Involucres are cone-shaped, 1 mm high, and glabrous, with 4 round glands around the edge, each with a white petaloid appendage which is a bit wider than the gland (or petaloid appendages absent); 5-10 staminate flowers.

Fruits: Capsules globose and 3-lobed, to 1.5 mm high, and glabrous; containing 3 ovoid, white to gray seeds, to 1.5 mm long, 3-angled and transversely 2-3-ridged.

Ecology: Found on arid hillsides and slopes, from 3,000-6,000 ft (914-1829 m); flowers August-October.

Distribution: s CA, s UT, AZ, s CO, NM, TX; south to n MEX.

Notes: This species belongs to the Chamaesyce subgenus of Euphorbia. Some treatments, even recent ones, continue to treat Chamaesyce as a separate genus even though molecular evidence places it within Euphorbia. Chamaesyce spp are distinct based on their leaves which are always opposite and and often have asymmetric bases; cyathia (flower structures) in leaf axils, not at branch tips, and usually with petaloid appendages; and stipules present and not gland-like. E revoluta is distinguished by being a delicate, erect, hairless annual with slender, linear leaves. The entire plant often has a reddish/maroon tint, and the stems fork evenly into two branches multiple times, with a pair of leaves and often a single cyathium (flower-like structure) at each fork point. It is wise to make a collection whenever ID to species is needed, as Chamaesyces are difficult to identify in the field, and multiple species of the genus will commonly grow side-by-side.

Ethnobotany: Used as a lotion for chafing and sores.

Etymology: Euphorbia is named for Euphorbus, Greek physician of Juba II, King of Mauretania; revoluta means rolled backwards, referring to the revolute margins of the meaves.

Editor: SBuckley 2010, FSCoburn 2015, AHazelton 2017

Plant: Erect annual forb 10-20 cm; herbage with milky sap; stems delicate

Leaves: cauline, opposite, short-petioled, linear, 1-2 cm long, with revolute margins; tip acute to obtuse

INFLORESCENCE: involucre < 1.5 mm, obconic, glabrous; gland < 0.5 mm, round, appendage wider than gland or 0, entire, white

Flowers: flowers monoecious borne in cyathia; petaloid appendages white; Staminate flowers 5-10, generally in 5 clusters around pistillate flower, each flower a stamen; Pistillate flower: 1, central, stalked; ovary chambers 3, ovule 1 per chamber, styles 3, divided 1/2 length

Fruit: capsule slightly < 1.5 mm, spheric, lobed, glabrous; Seeds 1-1.5 mm, ovoid, 3-angled, white with transverse wrinkles

Misc: Rocky slopes; < 3100 m.; Aug-Sep