Euphorbia hirtula Engelmann ex S. Watson in W. H. Brewer et al., Bot. California 2: 74. 1880; Chamaesyce hirtula (Engelmann ex S. Watson) Millspaugh; C. serpillifolia (Persoon) Small subsp. hirtula (Engelmann ex S. Watson) Koutnik; E. serpillifolia var. hirtula (Engelmann ex S. Watson) L. C. Wheeler

Stems pilose or villous. Leaves: petiole and blade pilose or villous. Involucre pilose or villous. Pistillate flowers: ovary pilose, villous, or glabrous. Capsules pilose, villous, or glabrous.

Flowering and fruiting summer–fall. Chaparral, oak woodlands, oak-pine forests, disturbed roadsides; 700–1900 m; Calif.; Mexico (Baja California).

Subspecies hirtula has a scattered and disjunct distribution primarily in montane areas of central and southern California and northern Baja California. In the flora area, it is found in the central Sierra Nevada and the Santa Lucia, San Bernardino, San Jacinto, Cuyamaca, and Laguna mountains.