BETULACEZ. SILVA OF NORTH AMERICA. 67 
ALNUS. 
FLOWERS unisexual, moncecious, apetalous, the staminate in long pendulous 
aments; calyx usually 4-parted; stamens usually 4; the pistillate in erect cylindrical 
aments; ovary naked, 2-celled; ovule solitary in each cell, suspended. Fruit a winged 
or wingless nut covered by the woody persistent scale of a strobile. Leaves alternate, 
generally serrate, stipulate, deciduous. 
Alnus, Linnzus, Gen. 285 (1737). — Endlicher, Gen. 272.— Clethropsis, Spach, Ann. Sci. Nat. sér. 2, xv. 201 (Revisio 
Meisner, Gen. 351. — Baillon, Hist. Pl. vi. 254. — Ben- Betulacearum) (1841). 
tham & Hooker, Gen. iii. 404. — Prantl, Engler & Prantl Semidopsis, Zumaglini, Fl. Pedem. i. 249 (1849). 
Pfhlanzenfam. iii. pt. i. 45. Alnobetula, Schur, Verh. Siebenb. Ver. Naturw. iv. 68 
Betula, Linnzus, Gen. ed. 6, 485 (in part) (1764). — Adan- (Enum. Pl. Trans.) (1858). 
son, Fam. Pl. ii. 375 (in part). — A. L. de Jussieu, Gen. 
409 (in part). 
Trees or shrubs, with watery juice, astringent scaly bark, soft straight-grained wood, terete 
branchlets marked with pale lenticels, often stoloniferous roots, and fibrous rootlets. Leaf-buds without 
scales, stipitate, elongated, slightly three-angled, oblong and acute, or clavate and rounded at the apex, 
formed in summer, nearly inclosed by the united stipules of the first leaf becoming in winter thick, 
resinous, dark red, and glabrous or scurfy-pubescent.' Leaves in the bud inclosed in their stipules, the 
lowest next the branch, open and convex, but becoming conduplicate or sometimes even revolute in 
expansion, plicately folded along the primary veins, alternate, penniveined, serrate, or rarely entire, 
petiolate, deciduous, falling without change of color, and leaving small semioval elevated leaf-scars 
displaying the ends of three equidistant fibro-vascular bundles. Stipules, except those of the first leaf, 
ovate, acute, scarious, deciduous. Flowers opening in the early spring before or with the unfolding of 
the leaves, or rarely in the autumn, monecious, sessile, in from one to six-flowered cymes in the axils of 
the peltate short-stalked scales of pedunculate aments formed in summer or autumn, the peduncles 
in the axils of the last leaves of the year or in those of minute leafy bracts. Staminate aments 
elongated, pendulous, panicled, or rarely solitary, in the axils of the last leaves or of leafy bracts, naked 
and erect during the winter ; scales usually three-flowered, rarely one-flowered, the flowers subtended by 
from three to five minute bractlets adnate to the base of the scale. Calyx usually four or irregularly 
from ten to twelve-parted. Stamens as many as the number of the divisions of the calyx or rarely half 
as many, inserted on its base opposite its divisions; filaments short or rarely elongated, undivided ; 
anthers erect, attached on the back, introrse, two-celled, the cells parallel, contiguous, opening 
longitudinally. Pistillate aments ovoid or oblong, erect, pedunculate, produced in summer in the axils 
of the leaves of a branch developed from the axil of one of the upper leaves of the year, below the 
staminate inflorescence, and inclosed at first by the stipules of its first leaf, emerging in the autumn 
and naked during the winter or remaining covered until early spring, or rarely solitary in the axil of 
an upper leaf; scales fleshy, two-flowered, the flowers subtended by from two to four minute bractlets 
adnate to the scale, becoming at maturity thick and woody, obovate, from three to five-lobed or 
truncate and thickened at the apex, and forming an ovoid or subglobose strobile persistent on the 
branch after the opening of its closely imbricated scales and the escape of the nuts. Nut minute, 
bright chestnut-brown, compressed, ovate, orbicular, or obovate, pointed and crowned at the apex with 
the remnants of the styles, truncate, and marked at the base with a pale umbilicus, wingless, or 
1 Henry, Nov. Act. Acad. Cas. Leop. xviii. 528, t. 39. 
