6.
Pinus strobiformis
Engelmann in Wislizenus, Mem. Tour N. Mexico. 102. 1848.
Southwestern white pine, Mexican white pine, pino enano
Pinus ayacahuite
Ehrenberg var.
brachyptera
G.R. Shaw;
P
.
ayacahuite
var.
reflexa
(Engelmann) Voss;
P
.
ayacahuite
var.
strobiformis
(Engelmann) Lemmon;
P
.
flexilis
E.James var.
reflexa
Engelmann;
P
.
reflexa
(Engelmann) Engelmann
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.
