434 



Butler: The western American birches 



13. Betula alaskana Sarg. Bot. Gaz. 31 : 236, 



1 90 1 



A tree reaching a height of 26 m. with bark varying from 

 nearly white to brown, separating more or less freely into layers ; 

 branchlets densely glandular-resiniferous ; leaf-blades 4-8 cm. 

 long and nearly as wide, triangular-ovate or deltoid, with long 

 acuminate apex and truncate base, coarsely serrate with abruptly 



Figure 13. Betula ulaskant. 



Figure 14. Betula papyrifera Marsh 



Sarg. From/ B. Tarletoni^g, YxomB. T. Butler 322, Big Fork, Mon- 

 Fort Selkirk, Yukon Territory. 



tana. 



pointed teeth, dull dark green above, paler beneath/ somewhat 

 hairy when young; petioles 15-30 mm. long, slender; fruiting 

 aments 3-3.5 cm. long, 8-12 mm. thick; bractlets glabrous or 

 puberulous, sometimes ciliate, lateral lobes spreading, wider but 

 scarcely longer than the narrow, triangular, acute middle one ; 

 samara wings broader than the small oval nutlet [Figure 13.] 



This species is distinguished by the very long-pointed leaves 

 and densely resinous branchlets. All the specimens I have seen 

 have dark brown bark not readily separating into layers and have 

 a very thin superficial outer layer. It is found from the Saskat- 

 chewan Valley to the Yukon, being common in the Yukon Basin. 



