432 



Butler : The western American birches 



with abruptly tipped teeth, veins 4 or 5 pairs; petioles 15-25 

 mm. long ; fruiting aments about 2 cm. long, 5 mm. thick ; bract- 

 lets about 3 mm. long, ciliate, the middle lobe rounded, slightly 

 narrower and as long as or but slightly longer than the erect 

 rounded lateral ones ; samara wings about as wide as the small 

 oblong nutlet. [Figure 10.] 



This is an Alaskan species found along the northwestern coast 

 and locally known as red or black birch. It resembles B, fonti- 

 nalis but has larger, more coarsely serrate leaves, less resiniferous 

 branchlets, separable bark, and entirely different fruiting aments 

 and bractlets. 



4 



II. Betula utahensis Britton, Bull. Torrey Club 31: 165. 



1904 



A small tree with dark yellowish-brown or bronze bark, not 

 separable into layers, lenticels pale gray and rough ; twigs and 

 branchlets slender, more or less densely glandular-resiniferous, 

 greenish- or reddish-brown, becoming very dark brown or gray, 



Figure i i . Betula utahensis Brit- 



FiGURE 12. Betula Piperi 



ton. From type, S, G. Stokes, City BriUon. From type, C. V. Piper 

 Creek Canyon, Salt Lake City,Utah. 3^2^, near Pullman, Washington. 



