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 cyUndric, 2-5 

 cm. long, with puberulent or cihate bracts. Papeb or Canoe Biech. — North- 

 eastern Wyommg, 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 arg 

 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 one 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 sUghtly ciliate : seed orbicular-winged. MoTj>fTAiN 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-hke 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. occidenialis. 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 la,rge, sharply double-toothed: aments begin their development the 

 summer preceding the season in which they open arid hang naked upon the 



