Artemisia spiciformis Osterhout var. longiloba Osterhout, Muhlenbergia 4: 69. 1908; A. longiloba (Osterhout) Beetle; Seriphidium arbusculum (Nuttall) W. A. Weber subsp. longilobum (Osterhout) W. A. Weber

Leaves broadly cuneate (4–10 × 2–5 mm, often irregularly lobed, lobes rounded, middle lobes overlapping lateral lobes). Involucres 2–3 × 1.5–2.5 mm. 2n = 18, 36.

Flowering early–late spring. Clay soils of alkaline basins and valleys, occasionally on outwash plains of mountains; 1500–2500 m; Calif., Colo., Idaho, Mont., Oreg., Utah, Wyo.

Subspecies longiloba is distinguished from other members of the Artemisia arbuscula complex by its early blooming time. It is the only member of subg. Tridentatae to begin flowering as snow melts in early spring, and it is ecologically distinguished from other subspecies by its occurrence at low elevations, in fine-grained clay soils.