Duration: Annual

Nativity: Native

Lifeform: Forb/Herb

General: Annual herb from a slender taproot; stems mostly prostrate and spreading, to 15 cm long; herbage covered with glistening gland-tipped hairs.

Leaves: Opposite along the stems, on petioles 1 mm long; blade oblong to ovate, 2-7 mm long, with an asymmetric base and entire margins; stipules distinct, filiform.

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. setiloba, the cyathia (flower structures) are solitary in the leaf axils near branch tips. Involucres are bell-shaped or urn-shaped, 1 mm high, and villous (hairy), with 4 red to pink glands around the edge, each with a white to pink petaloid appendage that is divided into 3-6 point-tipped triangular segments; 3-7 staminate flowers.

Fruits: Capsules globose and sharply angled, 1 mm diameter, pubescent; containing 3 tan to cream colored quadrangular seeds, to 1 mm long, dimpled or with faint ridges.

Ecology: Found in canyons and on plains from 200-5,000 ft (61-1524 m); flowers March-October.

Distribution: c and s CA, s NV, s UT, AZ, s NM, s 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. setiloba is a prostrate (ground-hugging) annual, distinguished by its leaves and stems with long, soft hairs which are usually gland-tipped and somewhat sticky (use your hand lens); small leaves less than 1.5 cm long with smooth edges; cyathia (flower structures) with red glands and white petaloid appendages which are divided into sharp-pointed triangular segments, making them resemble stars; and hairy seed pods. 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: Unknown

Etymology: Euphorbia is named for Euphorbus, Greek physician of Juba II, King of Mauretania; setiloba means bristle-lobed; alluding to the sharp-pointed petaloid appendages.

Synonyms: Chamaesyce stiloba, Euphorbia floccosiuscula

Editor: LCrumbacher 2011, FSCoburn 2015, AHazelton 2017

Plant: Prostrate annual forb branching from central point; herbage pubescent, with milky sap

Leaves: cauline, opposite, inequilateral at base, with entire margins

INFLORESCENCE: inflorescence (cyathium) urceolate; involucre < 1.5 mm, urn-shaped, hairy; gland < 0.5 mm, oblong, appendage wider than gland, 3-5-lobed, white

Flowers: petaloid appendages white, deeply parted into attenuated segments; Staminate flowers 3-7, 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 to base

Fruit: capsule, < 1.5 mm, spheric, pubescent; Seeds ± 1 mm, ovoid, white to brown, smooth

Misc: Sandy places; < 1500 m.; Most of year

Notes: Flowers borne of a cyanthia. Cyanthia with 3-5 petaloid appendages, about 1mm long. Each white, with red glands, and wider than the glands.Involucre about 1mm long. Staminate flowers 3-7, pistallate flowers 1.Plant armed with stinging hairs.Foliage pale green. Stems pubescentSeeds brownish and quadrangular.

References: Kearney & Peebles; Arizona Flora. ASU specimans