Perennials totally glabrous. Roots slightly fusiform—thickened, up to 3 cm in diameter. Caudex (rhizomes) up to 8 cm long. Stems 40-70 cm tall, entirely green, up to 1.2 cm in diameter, usually with sterile or fertile branches. Lower leaves ternate, very occasionally nearly biternate; petioles 4-13 cm long; leaﬂets 3 in number, each leaﬂet with three or several segments, each segment with two or several lobes, rarely entire, segments and/or lobes totalling 33-78 in number; segments 3-8 cm long, 0.4-2.0 cm wide; lobes linear to lanceolate, usually acute, sometimes mucronate at the apex, 0.2-3.0 cm long, 0.2-1.2 cm wide. Flowers terminal, solitary but usually several, up to 6 in number on a stem, pendent; involucrate bracts usually 1 or 2 in number, leaf-like; sepals 3 or 4 in number, rounded, green or green but purple at the periphery, or purple, 1.2-2.0 cm long, 1.2-2.0 cm wide, as large as or slightly smaller than petals; petals 6-8 in number, entire, purple, dull dark red, dark purple red or brownish purple, 1.2-2.2 cm long, 1.0-2.0 cm wide: stamens numerous; filaments yellow; anthers yellow; disk ﬂeshy, yellow, dentate, teeth variable in shape, 2.5-6 mm high; carpels 3, less frequently 2, occasionally 4, 5 or 6 in number, glabrous; stigmas sessile, 3 mm long, 2 min wide, horizontal. Follicles cylindrical, 2.5-4.2 cm long, 1.1-1.7 cm in diameter. Seeds oblong, black, 10-12 mm long, 5.5-6 mm in diameter.
Chromosome number: 2n = 10 (diploid).
Growing from coastal areas with altitudes of only 30 m to mountain areas with altitudes up to 1,200 m at Corte Madera Ranch, San Diego County. It occurs mostly in chaparral, or openings, or on edges of chaparral and Quercus Woods, with Adenostemma fasciculata, Erodictyon crassifolium, Eriogonum fasciculata, Rhus laurina, Salvia mellifera and Artemisia californica most frequently found as associated plants. It prefers dry granite soils. Conﬁned to the northern-most Baja California of Mexico and to S California, USA.
Paeonia californica is recognised as an independent species by most taxonomists. However, Brewer and Watson (1876), Jepson (1909, 1923) and Munz (1935) treated it as synonymous with P. brownii Douglas ex Hook., Whereas Lynch (1890) reduced it to a variety of P. brownii. Stebbins (1938) clearly documented the distinctness of P. californica from P. brownii, but Halda (1997, 2004) still recognised the former as a subspecies within the latter. We made ﬁeld observations and carried out population sampling in 2005 in southern California with the assistance of Dr J. Z. Qiu, and in the Blue Mountains guided by Paige Woodward from Canada. We sampled two populations in California and three in Oregon. In addition, we conducted ﬁeld observation on P. brownii in 1999 in Idaho, guided by Dr jenny Q. Y. Xiao. According to our observations and population samples, the lower leaves of P. californica are always ternate, a unique aspect in the genus, whereas they are always biternate in P. brownii. The carpels number mostly three (27/34, i.e. 80%), less frequently two, occasionally four, five or six in P. californica, but mostly ﬁve (29/39, i.e. 74.4%), rarely four, very occasionally six or three in P. brownii. The number of ﬁnal lobes on the lower leaves ranges from 33 to 78 in P. californica and 59—110 in P. brownii, and these two ranges are statistically discontinuous. Our cluster analysis (the unweighted pair-groups method using arithmetic averages, i.e. UPGMA) shows that these two entities are morphologically distinct and should be better treated as two separate species.
- Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, pp. 103-105.