Perennials, glabrous throughout except for leaf margins. Roots all slightly fusiform, up to 2.4 cm in diameter, brown—black outside. Caudex (rhizomes) up to 12 cm long, 0.6—1.3 cm in diameter; stems 15-48 cm tall, up to 1 cm in diameter, with 5-7 scales at the base, usually with no branches but sometimes with fertile or sterile branches. Lower leaves biternate with 9 leaflets, petioles 3—7 cm long; each leaflet with several segments, each segments with several final lobes; segments 0.3-2.0 cm wide; final lobes 59—110 in total, oblong or ovate-lanceolate, rounded or acute, sometimes mucronate at the apex, 0.2—1.2 cm wide, margins thickened and recurved, sometimes with bristles. Flowers terminal, solitary or up to 4 on a stem, pendent; involucrate bracts 1-2 in number, leaf-like; sepals 3-5 in number, green or purple or green but purple at the periphery, more-or-less larger than petals, rounded, 1-2.2 cm long, 1.1-2.1 cm wide; petals 7-10 in number, orbicular, red-brown or brown-purple, often yellow at the periphery, entire, 0.8-1.5 cm long, 0.6-0.9 cm wide, incurved and never fully expanded; stamens numerous; filaments pink, anthers yellow; disk fleshy, dentate, 3 mm high; carpels mostly 5, rarely 4, very occasionally 6, 3 or 2 in number; stigmas sessile, 1.5-1.9 mm long, c. 1 mm wide, purple, horizontal. Follicles cylindrical, 2-4 cm long, 1.2-1.9 cm in diameter. Seeds black, oblong, 10-12 mm long, 6-6.5 mm in diameter.
Chromosome number: 2n=10 (diploid)
Usually growing in sparse chaparral, open places in chaparral or woods of Pinus, Picea or Populus, or on grassy slopes. The plants with which it is most frequently associated are Pinus ponderosa, Pseudotsuga menziesii, Calocedrus decurrens, Populus tremuloides, Larix sp., Castanopsis sp., Ceanotus sp. and Artemisia spp. The species mostly occurs in granite soils or on volcanic rocks at altitudes from 600 to 2,600 m. Confined to the USA and distributed in N California, Idaho, Nevada, Oregon, Utah, Washington and Wyoming.
Of the two species in sect. Onaepia, Paeonia brownii is distinct with lower leaves having 9 leaflets, carpels mostly 5, less frequently 4 in number, and petals always smaller than sepals. The two species are allopatric.
- Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, pp. 97-98.