60 MISC. PUBLICATION 4 2 3, U. S. DEPT. OF AGRICULTURE 



Pines suffer considerably from the ravages of bark beetles. Species 

 of the white pine group, with normally 5 needles in the fascicle (P. 

 aristata, P.flexilis, P. strobiformis) , are likely to be attacked by blister 

 rust if that destructive fungus should reach Arizona. 



Key to the species 



1. Leaves commonly less than 5 cm. long, usually strongly incurved, the margins 

 entire or very nearly so; trees small (2). 

 2. Fascicles mostly 5-leaved; bark of young trees smooth, white; sheaths per- 

 sistent 1 or 2 years, soon revolute; leaves very densely crowded toward 

 the ends of the branches, stout, deep green; cones 6 to 10 cm. long, 

 commonly at least 1H times as long as wide, cylindric or cylindric-ovoid, 

 at maturity deep brown purple; scales bearing a slender, deflexed, de- 

 ciduous prickle about 5 mm. long 4. P. ARISTATA. 



2. Fascicles seldom more than 3-leaved; bark of young trees not white; sheath 



soon deciduous, short, revolute; cones usually less than 6 cm. long, little 



if any longer than wide, broadly ovoid or nearly globular, light brown at 



maturity; scales usually muticous, the prickle, if any, very stout, strongly 



deflexed, and not more than 1 mm. long; seeds edible: Pinyons, nut 



pines (3). 



3. Leaves commonly in 3's, seldom more and often less than 1 mm. wide, 



deep bluish green (at least on young trees) and strongly glaucous on 



the ventral face, usually very crowded toward the ends of the 



branches 1. P. cembroides. 



3. Leaves commonly in 2's or single, commonly more than 1 mm. wide, yel- 

 lowish green or sometimes moderately glaucous, usually not very 

 crowded (4) . 

 4. Leaves commonly in 2's, semiterete, deeply channeled- _ 2. P. edulis. 



4. Leaves mostly single, terete 3. P. monophylla. 



1. Leaves usually more than 5 cm. long, straight or only slightly incurved (5). 



5. Fascicles 5-leaved; leaves slender, the margins entire or very obscurely and 



remotely serrulate; sheaths deciduous; cones at maturity cylindric or 



cylindric-ovoid, at least lli times as long as wide, 8.5 to 25 cm. long, 



pendent; scales muticous; bark of young trees silvery gray; branches often 



drooping: White pines (6). 



6. Cone scales broadly truncate at apex, the tip not or scarcely reflexed; 



trunk short, branched nearly from the ground; leaves yellowish 



green 5. P.flexilis. 



6. Cone scales narrowed toward the rounded apex, the tip strongly re- 



flexed; trunk of mature trees well developed and clear of branches 

 to a considerable height, often tapering rapidly; leaves bluish 



green 6. P. strobiformis. 



5. Fascicles normally 3-leaved (except in P. arizonica) ; leaves dark yellowish 

 green, the margins minutely but distinctly and closely serrulate; cones 

 at maturity ovoid to nearly globular, seldom more and usually less than 

 V/2 times as long as wide; scales bearing a short, stout, deflexed prickle; 

 bark of young trees not silvery gray, that of older trees deeply and nar- 

 rowly furrowed (7) . 



7. Sheaths soon deciduous ; leaves 5 to 12 cm. long, about 1 mm. wide ; cones 4 to 



7 cm. long, on a stalk 10 to 15 mm. long, this often falling with the cone; 



prickles of the cone scales gradually deciduous 7. P. leiophylla. 



7. Sheaths persistent; leaves 10 cm. long, or longer; cones 5 to 15 cm. long, 

 subsessile, the basal scales usually persistent on the branch after the 

 cone falls; prickles of the cone scales persistent: Yellow pines (8). 

 8. Leaves usually more than 25 (up to 37) cm. long, about 2 mm. wide; 



sheaths 20 to 35 mm. long 10. P. latifolia. 



8. Leaves 10 to 20 (rarely 25) cm. long; sheaths mostly 10 to 20 mm. long 

 (9). 

 9. Fascicles commonly 3-leaved; leaves mostly 1.5 mm. wide; cones 7 to 



15 cm. long 8. P. ponderosa. 



9. Fascicles mostly 5-leaved; leaves about 1 mm. wide; cones 5 to 9 

 cm. long_^ ,. 9. P. arizonica. 



