BETULACfi^ 



Flowers opening in winter or early spring before the unfolding of the leaves; pistillate 



aments usually naked during the winter. 



Wing of the nut broad; leaves ovate or elliptic, rusty-pubescent on the lower surface; 

 pistillate aments often inclosed during the winter; stamens 4. 2. A. rubra (B, G). 

 Wing of the nut reduced to a narrow border. 



Stamens 4; leaves oblong-ovate, glabrous or puberulous on the lower surface. 



3. A. tenuifolia (B, F, G). 

 Stamens usually 2, or 3. 



Leaves ovate or oval. 4. A. rhombifolia (B, F, G). 



Leaves oblong-lanceolate, acute. 5. A. oblongifolia (H). 



Flowers opening in autumn from aments of the year; stamens 4; wing of the nut reduced 



to a narrow border; leaves oblong-ovate or obovate, dark green and lustrous above, 



pale yellow-green below. 6. A. maritima (A). 



1. Alnus sinuata Rydb. Alder. 



Alnus sitchensis Sarg. 



Leaves ovate, acute, full and rounded and often unsymmetrical and somewhat oblique 

 or abruptly narrowed and cuneate at base, divided into numerous short acute lateral lobes, 

 sharply and doubly serrate with straight glandular teeth, glandular-viscid as they unfold, 

 at maturity membranaceous, yellow -green on the upper surface, pale and very lustrous on 



Fig. 209 



the lower surface, glabrous, or villose along the under side of the stout midrib with short 

 brown hairs also forming tufts in the axils of the numerous slender primary veins, 3'-6' 

 long, H'-4' wide; petioles stout, grooved, abruptly enlarged at the base, ^'-f in length; 

 stipules oblong to spatulate, rounded and apiculate at apex, puberulous, about \' long. 

 Flowers : staminate aments sessile, in pairs in the axils of the upper leaves sometimes re- 

 duced to small bracts, and single in the axil of the leaf next below, during the winter about 

 $' long and \' thick, with dark red-brown shining puberulous apiculate scales, becoming 

 when the flowers open from spring to midsummer 4' or 5' long, with a puberulous light red 

 rachis and ovate acute apiculate 3-flowered scales; calyx-lobes rounded, shorter than the 

 4 stamens; pistillate aments in elongated panicles, inclosed during winter in buds formed 

 the previous summer in the axils of the leaves of short lateral branchlets, long-peduncu- 

 late, %' long, y thick. Fruit: strobiles on slender peduncles in elongated sometimes leafy 

 panicles 4'-6' in length, oblong, |'-f ' long, about $-' thick, their truncate scales thickened 

 at the apex; nut oval, about as wide as its wings. 



