BETULACER, SILVA OF NORTH AMERICA. 7 
ALNUS RHOMBIFOLIA. 
Alder. 
LEAVES ovate or oval, pale and slightly puberulous on the lower surface. Stamens 
usually 2. 
Alnus rhombifolia, Nuttall, Sylva, i. 33 (1842). — Torrey, Death Valley Exped.).—S. B. Parish, Zoé, iv. 347.— 
Bot. Wilkes Explor. Exped. 467.— Brewer & Watson, Greene, Man. Bot. Bay Region, 298. 
Bot. Cal. ii. 80 (in part). —Sargent, Forest Trees N. Am. Alnus oblongifolia, Watson, Brewer & Watson Bot. Cal. 
10th Census U. S. ix. 163 (in part).— Parry, Bull. Cal. ii. 80 (in part) (not Torrey) (1880).— Sargent, Forest 
Acad. ii. 351 (in part). — Mayr, Wald. Nordam. 286, Trees N. Am. 10th Census U. S. ix. 163 (in part). 
t. 5. — Coville, Contrib. U. S. Nat. Herb. iv. 195 (Bot. 
A tree, frequently seventy or eighty feet in height, with a tall straight trunk from two to three 
feet in diameter, long slender branches pendulous at the extremities, and a wide round-topped open 
head. The bark on old trunks is about an inch in thickness, dark brown, and irregularly divided into 
flat and often connected ridges, which are broken into oblong plates and are scaly on the surface with 
small closely appressed scales. The branchlets are slender and marked with small scattered lenticels, 
and when they first appear are ight green and coated with pale caducous pubescence, but soon become 
dark orange-red and glabrous, and grow darker during the winter and the following summer. The 
buds are nearly half an inch long, very slender, dark red, and covered with pale scurfy pubescence. 
The leaves are ovate or oval, or sometimes nearly orbicular, rounded, or acute, especially on vigorous 
shoots, at the apex, gradually or abruptly narrowed and wedge-shaped at the base, finely or sometimes 
coarsely and occasionally doubly serrate with small spreading glandular teeth, and slightly thickened 
and reflexed on the somewhat undulate margins; when they unfold they are pale green and coated with 
deciduous matted white hairs; and when fully grown they are dark green and lustrous on the upper 
surface, which is frequently marked, especially along the midribs, with minute black glandular dots, light 
yellow-green and slightly puberulous on the lower surface, from two to three and a half inches long 
and from one and a half to two inches wide, with stout yellow midribs and primary veins, conspicuous 
reticulate cross veinlets and slender yellow hairy petioles flattened and grooved on the upper side and 
from one half to three quarters of an inch in length. The stipules are ovate, acute, scarious, puberu- 
lous, and about a quarter of an inch long. The aments of staminate flowers are borne in slender- 
stemmed pubescent racemes and are usually short-stalked; during the summer they are dark olive-brown, 
and lustrous, from three quarters of an inch to an inch in length and about a sixteenth of an inch 
thick ; beginning to lengthen late in the autumn before the leaves have fallen, they are fully grown 
early in January, when they are from four to six inches long and a quarter of an inch thick, with 
dark orange-brown scales, and fall in February before the appearance of the new leaves. The calyx 
is yellow, with four ovate lobes rounded at the apex and rather shorter than the stamens, which are two 
or occasionally three in number or rarely single. The pistillate aments are borne in short pubescent 
racemes and emerge from the bud in December, and in January the styles protrude from between 
their broadly ovate rounded scales, and the ovaries are fertilized. The strobiles, which are oblong 
and from one third to one half of an inch in length, with thin scales slightly thickened and lobed at the 
apex, are fully grown at midsummer, but do not open and discharge their nuts until the trees are in 
flower in the following year. The nut is broadly ovate with a thin acute margin. 
Alnus rhombifolia inhabits the banks of streams and is distributed from northern Idaho to the 
