Purshia tridentata

(Pursh) de Candolle

Trans. Linn. Soc. London 12: 158. 1818.

Common names: Bitterbrush
Basionym: Tigarea tridentata Pursh Fl. Amer. Sept. 1: 333, plate 15. 1813
Treatment appears in FNA Volume 9. Treatment on page 340. Mentioned on page 339, 341.

Shrubs, evergreen or partially summer–winter-deciduous, 2–25(–40) dm. Stems: young-stem internodes 4–12 mm, sparsely to densely arachnoid-villous, ± hirtellous, or glabrous, stipitate-glandular or not; short-shoot spurs simple or branched, 5–20(–60) × 1.5–2 mm. Leaves: blade of 1 or 2 types: (1) persistent, dark green adaxially, obovate to spatulate, 4–9 × (1–)3–6 mm, irregularly lobed in distal 1/3, lobes 3(–5), lobes entire, ± terete, central lobe deflexed, often apiculate, 2 lateral ascending, margins strongly revolute, abaxial surface arachnoid-villous, midvein glabrous, glabrate, or hirtellous, adaxial glabrous, sometimes arachnoid-villous or hirtellous, often glandular-punctate along margins; (2) winter deciduous, green-gray adaxially, flabelliform, 6–15+ × 3–7+ mm, margins weakly revolute, usually 3-toothed, sometimes 3-lobed, distally, abaxial surface arachnoid-villous to arachnoid-tomentose, veins ± glabrate, adaxial hirtellous and ± arachnoid villous, sometimes sessile or stipitate-glandular along margins. Pedicels 0.2–2.5 mm. Flowers: hypanthium obconic, 2.5–5 × 1.5–3 mm, 3.5–6 mm diam. in fruit, pubescent-sericeous, sessile or stipitate-glandular; petals usually lemon- to cream-yellow, sometimes nearly white, obovate-spatulate, 4–7+ mm; stamens 17–35; carpels 1 or 2. Achenes broadly obovoid-fusiform (circular in cross section or flattened on common side when paired), 7–12 × 3.5–5.2 mm, 15–22-veined, persistent style 5–7(–10) mm, densely hirtellous.


V9 557-distribution-map.jpg

B.C., Ariz., Calif., Colo., Idaho, Mont., N.Mex., Nebr., Nev., Oreg., Utah, Wash., Wyo., nw Mexico.


Varieties 2 (2 in the flora).

Selected References



1 Leaves dimorphic, blades flabelliform, thin, margins weakly revolute, usually 3-toothed, sometimes 3-lobed, apically, adaxial surfaces persistently arachnoid-villous and hirtellous, margins rarely with sessile or stipitate glands, these not strongly resinous, (at least proximalmost short-shoot leaves, smaller, thick, 3-lobed distally, margins with or without resinous glands); stems: young long shoots arachnoid-villous to pubescent, stipitate-glandular or not. Purshia tridentata var. tridentata
1 Leaves monomorphic, blades obovate, coriaceous-thickened, 3(–5)-lobed, lobes oblong-linear, central lobes deflexed, 2 lateral ascending, margins strongly revolute, adaxial surfaces glabrous, sometimes weakly arachnoid-villous or hirtellous, margins often with large, resiniferous, punctate glands; stems: young long shoots glabrous or sparsely hirtellous, often stipitate-glandular. Purshia tridentata var. glandulosa