| Leaves usually entire, the stomata dorsal and ventral | 4. flexilis. |
| Leaves serrulate, the stomata ventral only | 5. Armandi. |
4. PINUS FLEXILIS
- 1823 P. flexilis James in Long's Exped. ii. 34.
- 1882 P. reflexa Engelmann in Bot. Gaz. vii. 4.
- 1897 P. strobiformis Sargent, Silva N. Am. xi. 33, tt. 544, 545 (not Engelmann).
Spring-shoots pubescent; branchlets very tough and pliant. Leaves from 3 to 9 cm. long, entire, or serrulate in the southern variety, persistent for five or six years; stomata dorsal and ventral or, in the south, sometimes ventral only; resin-ducts external. Cones from 6 to 25 cm. long, ovate or subcylindrical, short-pedunculate; apophyses pale tawny yellow, or yellow ochre, lustrous, often prolonged and more or less reflexed, thick, the margin together with the umbo raised above the surface of the cone.
This species grows on the Rocky Mountains from Alberta in the Dominion of Canada to Chihuahua in northern Mexico and ranges westward to the eastern slope of the Sierras and to the southern mountains of California. The wood, where accessible, is manufactured into lumber. It may be seen in the Arnold Arboretum and in the Royal Gardens at Kew.
P. flexilis is recognized by its lustrous yellow cones. This and the constantly external ducts of its usually entire leaves distinguish it from P. Armandi. From P. albicaulis, with similar leaves, it differs by its dehiscent cone. At one extreme the cone of P. flexilis is not unlike that of P. albicaulis, at the other extreme it approaches the characteristic cone of P. ayacahuite, with prolonged reflexed scales. Hence the confusion of P. albicaulis with P. flexilis (Murray, Parlatore and others) and of P. flexilis with Engelmann's P. strobiformis. Sargent's P. strobiformis, illustrated in the Silva of North America, is the form of this species known as var. reflexa of Engelmann.
Fig. 93, Two cones and seed. Fig. 94, Leaf-fascicle. Fig. 95, Magnified leaf-section.