The Parry Pinyon (Pinus quadrifolia) is a pine in the pinyon pine group, native to southernmost California in the United States and northern Baja California in Mexico, from 33° 30' N south to 30° 30' N. It occurs at moderate altitudes from 1300–1800 m, rarely as low as 1200 m and as high as 2500 m. It is scarce and often scattered in this region, forming open woodlands, usually mixed with junipers.
It is a small to medium size tree, reaching 8–15 m tall and with a trunk diameter of up to 40 cm, rarely more. The bark is thick, rough and scaly. The leaves ('needles') are in fascicles of 4–5, moderately stout, 2.5–5.5 cm long; glossy dark green with no stomata on the outer face, and a dense bright white band of stomata on the inner surfaces. The cones are globose, 4–5.5 cm long and broad when closed, green at first, ripening yellow to orange-buff when 18–20 months old, with only a small number of thick scales, with typically 5–10 fertile scales. The cones open to 5–7 cm broad when mature, holding the seeds on the scales after opening. The seeds are 10–14 mm long, with a thin shell, a white endosperm, and a vestigial 1–2 mm wing; they are dispersed by the Pinyon Jay, which plucks the seeds out of the open cones. The jay, which uses the seeds as a food resource, stores many of the seeds for later use, and some of these stored seeds are not used and are able to grow into new trees.
It frequently hybridises with Single-leaf Pinyon where their ranges meet in southern California and northern Baja California; the hybrids are distinguished by intermediate features, with needles usually fascicles of 2–3 with some stomata on the outer surface. It has been suggested by some botanists that the holotype specimen of P. quadrifolia is itself from a hybrid; presumed pure, non-hybrid specimens having been given a new name Pinus juarezensis (Juarez Pinyon, after the Sierra Juarez mountains of northern Baja California). However, there is no proof that these specimens are genetically 'purer' than the original type specimen, and few botanists accept P. juarezensis as other than a synonym of P. quadrifolia.
Despite the ease of hybridisation with Single-leaf Pinyon, Parry Pinyon is genetically probably more closely related to the Johann's Pinyon and Potosi Pinyon, despite being separated from them by well over 1000 km.