Trees or shrubs with deciduous stipules. Lark separating into thin layers. Leaves alternate, simple, with the veinlets running straight to the margin. Flowers monoecious, amentaceous, mostly naked, 3 in the axil of a 3-lobed bract. Stamens definite, distinct. Anthers 2-celled. Ovary 2-celled, 2-ovuled, becoming in fruit 1-celled and l-seeded (by abortion) membranous and indehiscent. Seed pendulous, without albumen. Figs. 11, 00, 106, 111, 419, 420.
Genera 2, species 65, chiefly natives of the cool parts of the northern hemisphere. Properties generally astringent. The birches are often fine timber trees.
1. BE'TULA, Tourn. Birch. (Beta is the Celtic name for the birch.) Flowers in a cylindric ament; bracts deeply 3-parted, peltate; calyx a scale ', stamens 4. Ament oblong-ovoid, scales trilobate; calyx 0; ovaries 3 under each scale; stigmas 2, filiform; nut compressed, with a membranous margin. - Trees and shrubs, with the outer bark laminated and horizontally fibrous, the inner aromatic. Branchlets dotted. Lvs. ovate, serrate. Figs. 419, 420.
* Trees with a yellowish bark, smoothish leaves, and short, erect, aments.......
* Trees with a reddish-brown bark and ovate-oblong, suberect, aments..........
* Trees with a white bark, long-stalked leaves and drooping aments..............
Nos. 4, 5
* Shrubs with brownish bark, roundish leaves and short erect, aments........
Nos. 6, 7
1 B. excelsa Ait. Yellow Birch. Lvs. ovate-elliptic, subacuminate; sub-cordate, coarsely, sharply, and doubly serrate, smooth when old, on short, downy petioles; fertile amenta erect, ovoid-oblong; lobes of the bracts subequal, acute, diverging. - A common forest tree, N. Eng. to Mich, and Can., arising in woods to the height of 60 to 80f, with a trunk 2 to 3f in diam., invested with a thin, yellowish, silvery outer bark stripping off in transverse shreds. Barren aments 2 to 4' long, cylindric, clustered, and pendulous at the ends of the branches; fertile 1' long, 6" diam. Apr., May.
2 B. lenta L. Black BIRCH. Sweet Birch. Mahogany Birch. (Fig. 202.) Lvs. cor date-ovate, acuminate, acutely, finely, and doubly serrate, veins beneath and petioles hairy; fertile aments erect, oval-oblong, thick, obtuse, pedunculate; scales hairy, the lobes obtuse, subequal, diverging. - This noble species is common in the Eastern and Middle States, often exceeding 60f in height, with a diameter of 2 to 3f. The trunk is invested with a dark brown or reddish bark, which becomes rough in old trees, and is remarkable for its agreeably aromatic fragrance and flavor. Leaves 3 - 4' long, about 1/2 as wide. Sterile aments 2 - 3' long, fertile much shorter and thicker. In spring the cambium affords the boys a delicious morsel Wood reddish, strong, compact. Apr., May,
3 B. nigra Ait Red Birch. Lvs. rhombic-ovate, acute at each end, doubly serrate, or obscurely 9 to 13-lobed, glaucous beneath; fertile ament sessile, erect, ovoid, scales villous, the segments linear, equal. - A treo 30 to 50f high, growing on banks of streams and in river swamps, Mass,, Ill, and Fla. (!) Trunk covered with a reddish or chocolate-colored bark which at length becomes very loose and torn, hanging in shreds, and finally rough like that of the black cherry. Branches arched and slender; branchlets almost filiform, often clothing the trunk to the base. Lvs. dark green above, about 3' by 2' often smaller, petioles 6 to 8" long, pubescent. May. (B. rubra Mx.)
4 B. populifolia Ait. Poplar-leaved Birch. White Birch. (Fig. 106.) Lvs. deltoid, long-acuminate, unequally serrate or obscurely many-lobed, very smooth, on smooth petioles; fertile nments pedunculate; scales with roundish, lateral lobes. - Like the next, distinguished for the white cuticle with which the trunk is invested. It is common in the rocky and mountainous woods of N. Eng., where it seldom exceeds 30 to 40f in height. The branches are covered with a reddish-brown bark, very slender, and throw out in May, long, pendulous aments.
5 B. papyracea Ait. Paper Birch. Canoe Birch. Lvs. ovale, acuminate, doubly serrate, the veins hairy beneath; fertile aments nodding, pedunculate: lateral lobes of the calyx short, roundish. - This birch is abundant in the hillside woods of N. Eng. to Wis. and Can. It sometimes attains the height of 60 - 70f but is generally smaller. Trunk 1 - 2f diam., covered with a tough cuticle consisting of numerous laminae, the outer of which is snow white. Of this the Indians construct their light canoes. Branches dark brown. Leaves 2 - 3' long, 1/2 as wide. Sterile aments 1 - 2' long. The wood is of a fine, compact texture, easily wrought. May, Jn.
β. minor. Lvs. smaller, ovate, glabrous, acute, some of them roundish-obtuse. - White Mts. Shrubs 6 - 9f high.
6 B. pumila L. Dwarf Birch. Shrub erect, its ascending branches glandular-punctate, glabrous; lvs. obovate, entire at base, obtusely serrate, glabrous; fertile ament cylindrical, about as long as the leaves; scales half 3-cleft, lobes ovate-oblong, middle one rather longest; nut orbicular, conspicuously margined. - A beautiful shrub inhabiting the mountainous districts of N. and N. W, States, N. to Hudson's Bay. Height 2 to 6f. Lvs. about 9" by 6 or 7", very regularly toothed. Aments of both kinds 7 to 9", (B. glandulosa Mx.)
7. B nana L. Tiny Birch. Shrub, low, trailing, smooth; lvs. orbicular, crenate, reticulated beneath; scales of the ament deeply 3-parted; seeds orbicular, nearly wingless. - This miniature tree is found on the summits of Mt. Clinton, Mt. Franklin, etc., of the White Mts. It is scarcely more than a foot in height, often but a few inches, the branches few and straggling, the lvs, 1/3 to 2/3' diam., smooth both sides pale and distinctly reticulate beneath, and on petioles 1 to 2" long, (B, Litttl-iana Tuckerman.)
3. AL'NUS, Tourn. Alder. (The ancient Latin name from Celtic al, near, lan, the river bank.) Aments cylindrie, drooping, the bracts with 5 bractioles beneath; calyx 4-parted; stamens 4, anthers 2-cellcd. Aments ovoid, bracts cuneate, truncate, fleshy, 2-flowered; calyx of 4 scales adnate below to the bracts, all persistent and woody in fruit; fruit compressed, wingless or winged. Shrubs arising from large and strong roots- Buds pedunculate. Lvs. plicate in vernation. Aments paniclcd. (Fig, 111.)
§ Fruit wingless, Nos, 1, 2.
§§ Fruit broadly winged. (Alnaster, Spach.) No.;;.
1 A. incana Willd. Speckled Alder Black Alder. Lvs. submembranous, oblong, acutish, obtuse at base or cordate, margin somewhat lobed, sharply serrate, glaucous-pubcscent beneath; veins hirsute, their axils naked; stip. oblonglanceolate; fertile aments oval. - Not uncommon along streams, N. Eng. to Wis. and Can. A tall shrub or small tree, readily distinguishable by the form and pubescence of the leaves. (A. glauca Mx.)
2 A. serrulata Willd. Smooth Alder. Lvs obovate, acuminate, doubly serrulate, smooth beneath, except the veins and their axils; stip. elliptical, obtuse. - A well known shrub growing in clumps, and forming thickets on the borders of ponds and rivers, and in swampa Stems numerous, rather straight, 10 - 15f in height Leaves 2 - 4' long and i as wide, strongly veined; petioles 1/3 - 1/2' long. Aments 2 - 3' long, slender, pendulous, fascicled at the ends of the branches; fertile ones short, thick, dark brown, persistent, several together a little below the sterile one. Mar., Apr. (A. rubra Tuckerman.)
3 A. viridis DC. Mountain Alder. Lvs. oval, acute, obtusish at base, doubly serrate, clothed with a soft viscid pubescence, or subglabrous, villous on the veins and axils beneath; stip. broadly ovate; fertile aments on long peduncles, oval. - High mountain streams, N. Eng. N. Y. and Can. An elegant shrub, 3 - 4f high. Leaves varying to broad-ovate, rarely cordate, nearly smooth in the alpine state, otherwise softly pubescent and sprinkled with resinous particles. Apr. (A. crispa Mx.)