74 BETULACEAE (BIRCH FAMILY) 



B. Bark often cracking in the direction of the tree circumference; lenticels elon- 

 gated in the direction of the tree circumference; winter buds covered by imbricate 

 scales; stamens 2, bifid; pistillate aments solitary; scales of pistillate aments 

 thin, 3-lobed. BETULA (p. 74) 



BB. Bark cracking up and down the tree or not at all; lenticels not elongated in 

 the direction of the tree circumference; winter buds inclosed by 2 scales; sta- 

 mens 4, not bifid; pistillate aments or cones in racemes; scales of pistillate aments 

 or cones thick, entire or erose or 5-toothed. ALNUS (p. 74) 



BETULA (BIRCH) 



Shrubs or trees. Leaves serrate or dentate, sometimes also lobed. Flowers 

 in aments, expanding before the leaves ; aments monoecious. Staminate 

 flowers about 3 in each scale axil, subtended by 2 bractlets ; scales entire ; 

 perianth membranous, usually 4-toothed; filaments 2-cleft, each fork 

 bearing i pollen sac. Pistillate flowers 1-3 on each scale; perianth none; 

 ovary sessile ; styles 2. Fruit a nutlet or samara, small, flat. (The Latin 

 name.) 



A. Branchlets not or very little warty-glandular. W. C. E. 



B. occidentalis (WESTERN BIRCH) 

 AA. Branchlets very much warty-glandular. 



B. Shrub or small tree, 3-12 m. high; leaves sparsely pubescent; body of the fruit 



much narrower than the wings. E. B. microphylla (ROCKY-MOUNTAIN BIRCH) 



BB. Shrub, 1-3 m. high; leaves glabrous; body of fruit as wide or wider than the 



wings. W. C. E. B. glandulosa (PEAT-BOG BIRCH) 



ALNUS (ALDER) 



Shrubs or trees. Leaves dentate or serrate, sometimes also slightly lobed. 

 Flowers in aments ; aments monoecious. Staminate aments fascicled, long- 

 cylindric ; flowers 3 or 6 on each scale ; perianth mostly 4-parted. Pistillate 

 aments oval or elliptic; flowers 2-4 on each scale; perianth none; ovary 

 sessile; styles 2. Fruit flat. (The Latin name.) 



A. Leaves doubly dentate or serrate, or more or less lobed and serrate; stamens 4. 



B. Teeth of leaves almost equilateral triangles; tip of tooth almost a right angle, 

 often with a gland; mature pistillate ament or cone 12-25 mm. long; leaves rusty- 

 pubescent beneath at least on the veins. W. C. A. oregona (RED ALDER) 



BB. Teeth of leaves rather narrow; tip of tooth acuminate or narrowly acute, 

 without gland; mature pistillate ament or cone 8-15 mm. long. 



C. Winter buds 12-13 mm. long, acuminate; leaves somewhat brown-hairy along 

 the veins beneath; stipules oblong to spatulate, 6-7 mm. long; pistillate aments 

 inclosed during the winter. W. C. E. A. sinuata (LATE ALDER) 



CC. Winter buds 6-9 mm. long, obtuse; leaves without brown hairs; stipules 

 ovate, 12-13 mra - long; pistillate aments naked during the winter. C. E. 



A. tenuifolia (MOUNTAIN ALDER) 



AA. Leaves simply serrulate, not at all lobed; stamens 1-3; mature pistillate ament 

 or cone 8-13 mm. long. E. A. rhombifolia (WHITE ALDER) 



