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Shrub or tree to 15 m, trunk short, often leaning or forked, 0.3–0.5 m dbh. Bark thick, dark reddish grey, scaly on lower trunk. Crown open, regular in young trees, becoming irregular with age. Branchlets stout, rough; vegetative buds 0.6–1 cm, pale buff, not resinous. Leaves in fascicles of (three to) four to five, persisting for three to seven years, slightly curved, rigid, epistomatic, dark green on outer face, glaucous blue-white on inner faces, triangular in cross-section, 3–5 × 0.1–0.15 cm, apex acute. Fascicle sheaths to 0.5–0.8 cm long, light buff-brown. Cataphylls 0.5–0.7 cm long, grey. Male strobili yellow, ovoid to subglobose, 0.5–0.8 cm long. Female cones subterminal, solitary or in whorls of two to three; peduncles short, nearly sessile, with semi-persistent cataphylls. Cones 4–6 × 4.5–7 cm, dark green, maturing yellow-brown to red-brown, mature in about 18 months; mature cones ovoid-conical to subglobose with rounded base, forming an irregular rosette when fully open. Scales 30–50 (of which 6–12 fertile), opening widely, weakly attached to cone rachis; apophysis pyramidal, yellow-brown to red-brown, smooth or finely wrinkled; umbo dorsal, 6–8 mm wide, flat to slightly raised, dark brown to grey with minute, deciduous prickle. Fertile seeds dark yellow-brown (infertile seeds pale buff), 1.2–1.8 × 0.8–1.2 cm; wings vestigial, remaining attached to seed scale. Perry 1991. Distribution MEXICO: northern Baja California; USA: southern California. Habitat Mountain ranges between 900 and 2700 m asl. USDA Hardiness Zone 8. Conservation status Lower Risk. Illustration Perry 1991. Cross-reference K234.
Pinus quadrifolia is related to P. monophylla (Malusa 1992, Gernandt et al. 2003) but also shows similarities to the P. johannis–P. culminicola group, with cones similar to the former and epistomatic foliage more like the latter. It hybridises extensively with P. monophylla in the wild; Lanner (1974) suggested that the type specimen of P. quadrifolia was one of these hybrids and described P. juarezensis to cover plants considered to be free of P. monophylla introgression, but this interpretation is rejected by Farjon & Styles (1997). There have been several introductions to cultivation. Harold Hillier received seed in the 1970s (K. Rushforth, pers. comm. 2007), which was probably the source of a specimen at the Hillier Gardens, and there is a young tree at Kew. The dark green and glaucous foliage makes it an attractive shrub or small tree, well suited to very dry conditions.