204 BETULACEAE 



7. B. fontinalis Sarg. A tree occasionally 10-12 m. high; often growing 

 in clumps and shrub-like; blades sharply double-serrate, entire towards the base, 

 soon glabrous, 2-5 cm. long; staminate aments 5-7 cm. long, several; pistillate 

 aments 2-3 cm. long; terminal lobe of the bractlets lanceolate, decidedly longer 

 than the lateral ones. B. occidentalis Nutt., not Hook. Mountain Birch, 

 Water Birch, Swamp Birch, Black Birch. River banks: Sask. — Neb. — 

 N.M.— Utah— Calif.— B.C.— Yukon. Plain—Mont. My-Je. 



8. B. montanensis Butler. A large tree; leaf-blades 4-6.5 cm. long, thick 

 and firm, slightly lobed, finely serrate, glabrous above, conspicuously hairy 

 beneath; fruiting aments 2.5-3.5 cm. long; bractlets 5-7 mm. long; middle lobe 

 triangular-lanceolate, acute. Lake shores: Mont. Subtnont. 



9. B. Sandbergii Britton. A shrub or shrub-like tree; leaf-blades up to 6 

 cm. long, thick, firm, dull bronze-green above, paler and sparsely hairy beneath, 

 rhombic-ovate or oval, acute at both ends; fruiting aments 2-4 cm. long, slender- 

 stalked; middle lobe of the bractlets longer than the ascending rounded lateral 

 ones. Black Birch. Swampy places: Sask. — Minn. — -Mont. Plain. 



10. B. Elrodiana Butler. A low shrub; twigs slender, red-brown or gray; 

 leaf-blades 1-3 cm. long, 1-2 cm. wide, oval or rhombic, rarely ovate or obovate, 

 often suborbicular, shining, dark green above, dull green and reticulate beneath; 

 fruiting aments 10-15 mm. long, 6-8 mm. thick, cyhndric or ellipsoid. Swampy 

 places: w Mont. Suhmont. 



11. B. obovata Butler. A coarse shrub; branchlets red-brown, becoming 

 gray; leaf-blades 2-4 cm. long, thick, firm, dark, shining above, paler and dull 

 beneath, serrate or crenate-serrate; fruiting aments cylindrical or oval, 2-2.5 

 cm. long, 6-8 mm. thick; middle lobe of the bractlets long, ovate or triangular, 

 obtuse, or acutish; lateral lobes obliquely rhombic. River banks: w Mont. 

 Suhmont. 



12. B. crenata Rydb. A shrub 2.5-4.5 m. high; branches puberulent and 

 reddish when young; leaf-blades shghtly pubescent when young, oval or elliptic, 

 1-3 cm. long, 8-20 mm. wide, crenate, dark green, shining, reticulate-veined 

 above; pistillate aments 12-18 mm. long, about 6 mm. thick; terminal lobe of 

 bractlets oblong or elliptic, obtuse or rounded at the apex; lateral lobes ascending, 

 obhquely ovate or rhombic, obtuse; nut oval, nearly 2 mm. long; wings of nearly 

 the same width. Lake banks: w Mont. Suhmont. Je. 



13. B. glandulifera (E. Regel) Butler. A shrub 1-5 m. high; leaf -blades 

 dentate-crenate, with rounded-ovate or on the vigorous shoots triangular teeth, 

 1.5-3 cm. long, sparingly hirsute when young, soon glabrous, dark green above, 

 yellowish or reddish green beneath; pistillate aments 1-2 cm. long, 6-7 mm. thick; 

 bractlets glabrous; lobes all oblong and obtuse at the apex, of nearly the same 

 length; wing one-fourth to one-half as wide as the oval nut. B. pumila glanduli- 

 fera E. Regel. Boggy places: Ont. — Wis. — Minn. — Sask. Plain — Suh)7iont. 

 My. 



14. B. glandulosa Michx. A shrub 0.3-2 m. high; twigs brown and 

 densely glandular-resiniferous; leaf -blades 1-2.5 cm. long, rounded at both ends 

 or sometimes acutish at the base, bright green above, paler beneath; staminate 

 aments u.sually solitary, 1-1.5 cm. long; pi-stillate aments 1-2.5 cm. long, 4-5 

 mm. thick; bractlets glabrous; lobes oblong, obtuse, the lateral ones shorter, 

 spreading, ascending and curved upward; wing of the samara very narrow. 

 Bog Birch, Scrub Birch. Wet places: Greenl. — Me. — Minn. — Colo. — Ore. — 

 Alaska. Suhmont. — Subalp. Je-Jl. 



2. ALNUS (Tourn.) Hill. Alder. 



Shrubs or trees, with astringent smooth bark. Staminate aments drooping; 

 calyx irregularly lobed; stamens as many as the lobes and oi)posite to them; 

 anthers introrse. Pistillate aments ovoid or oblong, cone-like; bracts subtend- 

 ing 2 flowers, becoming woody, truncate or lobed at the apex, persistent. Fruit 

 minute, nut-like, winged or wingless, with thin outer coat. Seeds solitary. 



