Trees to 30m; trunk to 0.9m diam., slender, straight; crown conic, becoming rounded to irregular. Bark gray, aging red-brown, furrowed, with narrow, irregular, scaly ridges. Branches spreading-ascending; twigs slender, pale red-brown, puberulous or glabrous, sometimes glaucous, aging gray or gray-brown, smooth. Buds ellipsoid, red-brown, ca. 1cm, resinous. Leaves 5 per fascicle, spreading to ascending-upcurved, persisting 3--5 years, 4--9cm ´ 0.6--1mm, straight, slightly twisted, pliant, dark green to blue-green, abaxial surface without evident stomatal lines, adaxial surfaces conspicuously whitened by narrow stomatal lines, margins sharp, razorlike and entire to finely serrulate, apex narrowly acute to short-subulate; sheath 1.5--2cm, shed early. Pollen cones cylindric, ca. 6--10mm, pale yellow-brown. Seed cones maturing in 2 years, shedding seeds and falling soon thereafter, pendent, symmetric, lance-cylindric before opening, broadly lance-cylindric when open, 15--25cm, creamy brown to light yellow-brown, stalks to 6cm; apophyses somewhat thickened, strongly cross-keeled, tip reflexed; umbo terminal, low. Seeds ovoid; body 10--13mm, red-brown, essentially wingless. 2 n =24. Arid to moist summit elevations, montane forests; 1900--3000m; Ariz., N.Mex., Tex.; n Mexico. In the northern part of the range, Pinus strobiformis overlaps P . flexilis and reportedly hybridizes with it. On average P . strobiformis has longer, more slender leaves and thinner, more spreading-tipped apophyses than are found in P . flexilis , and stomatal bands are not evident on the abaxial surface of its leaves.
FNA 1993, Perry 1991, Martin and Hutchins 1980, Kearney and Peebles 1969
Common Name: southwestern white pine Duration: Perennial Nativity: Native Lifeform: Tree General: Tree reaching 30 m with a diameter up to 1 m, slender, straight, with conic crown, becoming rounded and irregularly branched, branches long, horizontal to pendent; bark thin, smooth, grayish when young and on large mature trees, dark grayish reddish brown, rough, divided into small, irregular, rectangular plates. Needles: In fascicles of 5 needles, slender, slightly twisted and flexible, 6-10 cm long, bright green in color, margins serrate with very small, widely spaced teeth, to razor-like and entire; sheaths 1.5-2 cm, early deciduous. Cones: Variable in size, ranging from 10-20 cm in length, rarely longer, 10-15 cm usually; pendent, cylindrical to conical, straight to slightly curved, very resinous, yellowish to ochre color when mature; on peduncle about 2 cm long, falling with cone. Seeds: Dark brown, 10-12 mm long, wingless though occasionally with a very short, rudimentary wing 1-2 mm long. Ecology: Found on rocky slopes with mixed trees species to uniform stands from 6,500-10,000 ft (1981-3200 m). Notes: Cones take two years to mature, easily to identify by the long narrow pendent ones with their upturned scales. Also pay attention to the rows of fine white lines on the inner surface of the needles. In the northern extension of its range, P. strobiformis overlaps and is thought to hybridize with P. flexilis, but usually the former has more slender needles. These two can also be distinguished by by the needles of P. strobiformis being bluish green and the cone scales narrow and strongly reflexed at the apex, where P. flexilis has needles that are more yellowish-green, and cone scales that are truncate at the apex, neither narrowed nor reflexed. Ethnobotany: The seeds were eaten. Etymology: Pinus is the ancient Latin name for pines, while strobiformis comes from the Greek strobilos, meaning anything twisted, especially a cone, perhaps in reference to the slight twisting of the cone. Synonyms: Pinus ayacahuite, Pinus flexilis var. reflexa, Pinus reflexa Editor: SBuckley, 2010