Duration: Annual

Nativity: Native

Lifeform: Forb/Herb

General: Annual herbs, 7-35 cm tall, from slender taproot; stems prostrate to ascending, often mat-forming; herbage glabrous, pilose, or villous. 

Leaves: Opposite along the stems, on petioles less than 1 mm long; blade ovate to obovate or oblong, 3-13 mm long and 2-7 mm wide, with an asymmetric base, often a red spot in the center, and the margin entire near the base and toothed near the tip; stipules distinct, 1-2 mm long, divided into 3–5 subulate to filiform segments.

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. serpillifolia, the cyathia (flower structures) are solitary or clustered in the nodes near branch tips, or in congested axillary branches. Involucres are cone-shaped, 1 mm high, and glabrous, with 4 yellow or pink glands around the edge, each with a white to pink petaloid appendage; 5-20 staminate flowers.

Fruits: Capsules broadly ovoid, 1.5 mm high, glabrous, pilose, or villous; containing 3 pink, light brown, or grayish seeds, these ovoid to narrowly ovoid, 4-angled in cross section, 1 mm long, smooth to dimpled or rugose (wrinkled).

Ecology: Found in pine forests, cottonwood-willow riparian forests, temperate deciduous forests, chaparral, grasslands, Joshua tree woodlands, desert scrub, juniper-sagebrush scrub, and disturbed areas; below 8,500 ft (2591 m); flowers summer-fall, or anytime in r

Distribution: N. Amer from CAN to MEX; S. Amer.

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. serpillifolia is widespread and variable, especially in regard to seed sculpturing. Look for a low, glabrous annual; with leaves less than 1.5 cm long and usually broadest above the middle when fresh, and leaf margins toothed on the upper half (near the tip) and entire on the lower half (near the leaf base); seeds which are smooth or only weakly wrinkled or ribbed; and stipules more then 1 mm long; the species is commonly ground-hugging (prostrate), but in New Mexico tends to grow upright, a form traditionally labeled Chamaesyce neomexicana but now subsumed into this taxon. FNA recognizes 2 subspecies: subsp serpillifolia is glabrous (hairless) and found throughout the species' range; subsp hirtula is hairy and only grows from the central California coast south to Baja California, MEX. 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. Many sources spell this species' name E. serpyllifolia but FNA uses the originally published spelling, E. serpillifolia.

Ethnobotany: The Zuni used it cathartic, an emetic, and to increase the flow of milk in a breastfeeding mother. The leaves were also chewed for the pleasant taste and used to sweeten corn meal.

Etymology: Euphorbia is named for Euphorbus, Greek physician of Juba II, King of Mauretania; serpillifolia means thyme-leaved, from serpyllum, an ancient Greek name for thyme.

Editor: AHazelton 2017