Artemisia tridentata

Nuttall

Trans. Amer. Philos. Soc., n. s. 7: 398. 1841

Synonyms: Seriphidium tridentatum (Nuttall) W. A. Weber
Treatment appears in FNA Volume 19. Treatment on page 516. Mentioned on page 407, 510, 511, 512, 515, 5.
Shrubs, 40–200(–300) cm (herbage gray-haired), aromatic; not root-sprouting (trunks relatively thick). Stems gray-brown, glabrate (bark gray, exfoliating in strips). Leaves persistent, gray-green; blades usually cuneate, (0.4–)0.5–3.5 × 0.1–0.7 cm, 3-lobed (lobes to 1/3 blade lengths, 1.5+ mm wide, rounded), faces densely hairy. Heads (usually erect, on slender peduncles) in paniculiform arrays 5–30 × 1–6 cm. Involucres lanceolate, (1–)1.5–4 × 1–3 mm. Phyllaries oblanceolate to widely obovate, densely tomentose. Florets 3–8; corollas 1.5–2.5 mm, glabrous. Cypselae 1–2 mm, hairy or glabrous, glandular.

Distribution

V19-876-distribution-map.gif

w North America, nw Mexico.

Discussion

Subspecies 4 (4 in the flora).

Artemisia tridentata has undergone considerable taxonomic revision in the past century and circumscription of subspecies remains a topic of considerable controversy. Workers in the field should be aware of the morphologic variation within the subspecies across the range of the species (i.e., approximately from the Sierra Nevada in the west to the plains of the Rocky Mountains in the east). Because rangeland managers and conservationists can often identify local morphologic and chemical races based on grazing or habitat preferences of wildlife and domestic animals, some impetus exists to further subdivide the subspecies within A. tridentata at the varietal level. This treatment of the species complex remains conservative in light of the need for further study. As to chemical differences among the subspecies, aroma is often used to distinguish subspecies in the field. Volatile resins in the plants are strongly aromatic and, when crushed, leaves have very distinctive (although not easily described) aromas.

Key

1 Shrubs 100–200(–300) cm (leaf blades: lengths usually 3+ times widths); heads in relatively broad, paniculiform arrays > 2
1 Shrubs 30–150 cm (leaf blades: lengths usually less than 3 times widths); heads in relatively narrow, paniculiform arrays > 3
2 Involucres 1.5–2.5 × 1–2 mm; deep, well drained (usually sandy) soils in valley bottoms, lower montane slopes along drainages Artemisia tridentata subsp. tridentata
2 Involucres 2–4 × 1–2 mm; loose, sandy soils of valleys and foothills Artemisia tridentata subsp. parishii
3 Shrubs, 60–80(–150) cm (crowns flat-topped); heads in arrays 10–15 cm; involucres 2–3 × 1.5–3 mm; mountains Artemisia tridentata subsp. vaseyana
3 Shrubs, 30–50(–150) cm (crowns rounded); heads in arrays 2–6(–8) cm; involucres (1–)1.5–2 × 1.5–2 mm; usually cold-desert basins and high plateaus, sometimes foothills Artemisia tridentata subsp. wyomingensis