BETULACEAE 

 Thinleaf Alder. Mountain Alder 



Alnus tenuifolia Nutt. 



HABIT. A shrub or small tree occasionally 30 feet high and 

 6-8 inches in diameter; crown narrow and round-topped. 



LEAVES. Ovate-oblong; 2-4 inches long; slightly, acutely 

 and laciniately lobed; doubly serrate; thin and firm; dark green 

 and glabrous above, pale yellow-green below. 



FRUIT. Nut nearly circular; wing reduced to thin, mem- 

 branaceous border; strobiles Vs-Vz inch long, obovoid-oblong; 

 scales truncate, much thickened, 3-lobed at apex. 



TWIGS. Slender; marked by few, large orange-colored len- 

 ticels. Winter buds; stalked, V^-Vz inch long, bright red, puber- 

 ulous. 



BARK. Thin; smooth; red-brown. 



SILVICAL CHARACTERS. Tolerant when young, becom- 

 ing intolerant with age; on banks of mountain streams; the 

 common alder of the Rocky Mountain region; closely related 

 and considered by some authors to be a synonym of the eastern 

 speckled alder, Alnus rugosa. 



* * * 



Sitka Alder 



Alnus sinuata (Regel) Rydb. {Alnus sitchensis Sarg.) 



HABIT. A shrub or small tree rarely 40 feet high and 7-8 

 inches in diameter; crown narrow and open. 



LEAVES. Ovate; 3-6 inches long; acute; usually divided into 

 numerous, short, lateral lobes; sharply and doubly serrate; 

 membranaceous; yellow-green above, pale below. 



FRUIT. Nut oval, about as wide as its wings; strobiles 1^2 -% 

 inch long and about Yi inch wide; truncate scales thickened 

 at apex; on slender peduncles; in elongated, leafy panicles. 



TWIGS. Slender; large, pale lenticels. Winter buds: sessile, 

 Yz inch long, acuminate, dark purple, finely pubescent. 



BARK. Thin; blue-gray; bright red inner bark. 



SILVICAL CHARACTERS. Tolerant when young, becom- 

 ing intolerant with age; in moist flats and along stream borders. 



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