Pinus monophylla Torr. & Frém.

Tree or shrub to 16 m, trunk straight at first in saplings, but with age often contorted and sometimes shrubby, up to 130 cm dbh. Bark thick, rough, fissured vertically and scaly, blackish grey. Crown broad, rounded or irregular, dense. Branchlets pale buff-brown, becoming grey; vegetative buds not or only slightly resinous. Leaves in fascicles of one (rarely two), persisting for four to ten years, grey-green to blue-glaucous (rarely duller green to yellow-green), amphistomatic, curved or nearly straight, stout, rigid, circular in cross-section, (2–)3–4.5(–5) × 0.16–0.23 cm, apex acute, margins (on two-leaf fascicles) entire. Fascicle sheaths 0.6–1.0 cm long, pale brown, bracts reflexing to form a rosette at the base of the fascicle by the second year. Cataphylls subulate or triangular, 0.3–0.4 cm long, orange-brown. Male strobili small, 0.5–1.0 × 0.3 cm, pollinating in spring. Female cones subterminal; single, paired or in whorls of three, mature cones sessile, or on a very short peduncule up to 2 mm long. Cones the largest and heaviest in subsect. Cembroides, (4–)5–8(–9.5) × (4–)5–8(–9) cm open, ovoid-conic, green, maturing yellowish buff, maturing in about 18 months, variably resinous. Scales 30–60, of which (1–)7–16 fertile (seed-bearing), irregular in shape, spreading widely on opening; apophysis pyramidal, greatly thickened and woody with a marked transverse ridge, rhombic to pentagonal, up to 32 mm broad; umbo dorsal, 8–12 mm wide, raised, with a minute prickle. Seeds large, 15–20(–22) mm long, 9–12 mm broad; seed shell thin; fertile seeds dark greyish, infertile seeds light brown; wings rudimentary, 1–2 mm long, remaining attached to the seed scale. Malusa 1992. Distribution USA: eastern California, Nevada, western Utah, and just into the far northwest of Arizona and the far south of Idaho. Habitat Arid, rocky slopes between 1000 and 2900 m asl. Very intolerant of shade; tolerant of drought. USDA Hardiness Zone 5–7. Conservation status Least Concern. Taxonomic note Pinus californiarum was only relatively recently distinguished from Pinus monophylla and is difficult to distinguish from it, it has nevertheless proved distinct in genetic analysis (Buck et al. 2020, 2023, Montes et al. 2019, 2022), and has a largely separate distribution to the south of P. monophylla with minimal overlap; they occur together in a narrow area from Joshua Tree National Park in Riverside County, California, to Red Rock Canyon National Park in Clark County, Nevada. The most reliable distinction is in leaf anatomy, with P. monophylla leaves having 2–7 resin canals, as opposed to 9–17 in P. californiarum. Other characters are less reliable, but overall, the leaves of P. monophylla tend to be sligtly stouter, and a strongly glaucous-blue tone rather than the duller, more greenish-grey of P. californiarum. The cones are also generally larger, though with much overlap. Hybrids with Pinus californiarum have also been detected genetically where their ranges meet in southern California, but have yet to be formally described (Buck et al. 2023). Hybrids also occur with P. edulis, found occasionally where they meet along the east edge of the range of P. monophylla (Buck et al. 2020, 2023). These hybrids have mixed leaf number and intermediate cones, larger than typical P. edulis.