140 BETULACEAE (BIRCH FAMILY) 



volucre of united bracts, much prolonged above the ovoid nut into a narrow 

 tubular beak, densely bristly. From Colorado to Washington; also northward 

 and eastward. 



2. BETULA L. BIRCH 



Outer bark usually separable in sheets, that of the branchlets dotted. 

 Twigs and leaves often spicy-aromatic. Staminate flowers 3, and bractlets 2, 

 under each shield-shaped scale or bract of the aments, consisting each of a 

 calyx of one scale bearing 2 two-parted filaments. Pistillate flowers without 

 bractlets or calyx. Bracts 3-lobed, becoming coriaceous and caducous. 

 Nutlets winged. 



Bark of trunk white or gray. 



Trunk single (simple at base; 1. B. papyrifera. 



Trunks few-several (in stools or clumps) . . . . . . 2. B. Andrewsii. 



Bark of trunk greenish-brown or brown. 



Low bushy shrub; nutlets orbicular- winged . . . . . 3. B. glandulosa. 



Taller and slender, becoming tree-like; nutlets with broad lateral wings 4. B. fontinalis. 



1. Betula papyrifera Marsh, Arb. Am. 19. 1785. A large tree eastward but 

 in our range much reduced: bark chalky-white, peeling into thin layers: leaves 

 ovate, acute, dentate and incised, glabrous above, pubescent on the veins 

 beneath: staminate aments slender, 5-10 cm. long; pistillate cylindric, 2-5 

 cm. long, with puberulent or ciliate bracts. PAPER or CANOE BIRCH. North- 

 eastern Wyoming, northward and eastward. 



2. Betula Andrewsii A. Nels. Bot. Gaz. 43: 281. 1907. Near B. papyrifera 

 but growing in clumps or stools, the coordinate trunks few to several, each 

 attaining a maximum diameter of 10-15 cm., after which they die and are 

 replaced by new shoots from the same root: bark on the old trunks silvery- 

 gray, exfoliating as in the preceding: branches reddish-brown, conspicuously 

 marked by the transversely disposed oval white lenticels; twigs pale brown: 

 leaves ovate, abruptly short-acuminate, sharply and irregularly serrate with 

 short teeth: fruiting bracts deeply 3-lobed, the middle oi\e longer and nar- 

 rower than the lateral: nut oblong-obovate, with very thin wings nearly twice 

 as broad as the body. Known only from type locality, Green Mountain, 

 Boulder, Colorado. 



3. Betula glandulosa Michx. Fl. Bor. Am. 2: 180. 1903. A low bush, 15- 

 20 dm. high or less, the dark-colored branches usually more or less resinous- 

 glandular: leaves small, obovate to oblong-obovate, mostly cuneate at base, 

 rounded and crenate above, smooth and often resinous-coated: the deeply 

 3-lobed bracts slightly ciliate : seed orbicular-winged. MOUNTAIN BOG BIRCH. 

 From California to Sitka, and eastward through British America to the 

 Atlantic, and southward in the mountains to New Mexico. 



4. Betula fontinalis Sarg. Bot. Gaz. 31: 239. 1901. Ranging in size from 

 a tree-like shrub to a tree 12 m. or more high, usually slender and freely 

 branched: bark smooth, dark; branches gracefully drooping: leaves thin, 

 broadly ovate, with small gland-tipped teeth, smooth above, lightly pubescent 

 beneath: wings of the nutlet as broad as the body. B. occidentalis. ROCKY 

 MOUNTAIN BIRCH. Throughout our range and westward 



3. ALNUS Gaertn. ALDER 



Shrubs or small trees with dentate or serrulate leaves, and flowers of both 

 kinds in aments. Sterile flowers 3, and bractlets 4 or 5 under each short- 

 stalked shield-shaped scale, consisting each of a 3-5-parted calyx and as 

 many stamens, with the filaments short and simple. Fertile flowers with a 

 calyx of 4 little scales adherent to the scales or bracts of the ament. 



1. Alnus tenuifolia Nutt. Sylva 1: 32. 1842. A large shrub or small tree, 

 usually several-stemmed from the base: leaves ovate, with prominent veins, 

 rather large, sharply double-toothed: aments begin their development the 

 summer preceding the season in which they, open and hang naked upon the 



