Alnus 957 



ALNUS TENUIFOLIA 



Alnus tenuifolia, Nuttall, Sylva, i. 32 (1842); Sargent, Silva N. Amer. ix. 75, t. 455 (1896), and 

 Trees N. Amer. 211 (1905); Winkler, Betulacece, 124 (1904); Schneider, Laubholzkunde, 133 

 (1904). 



Alnus incana, Moench, var. glauca, Regal, MSm. Soc. Nat. Mosc. xiii. 154 (1861) (in part). 



Alnus incana, Moench, var. virescens, Watson, in Brewer and Watson, Bot Calif, ii. 81 (1880). 



Alnus occidentalis, Dippel, Laubholzkunde, ii. 158 (1892) ; De Wildeman, Icon. Select. Hort. Thenensis, 

 ii- 147, t. 75 (1901). 



A tree attaining 30 feet in height and 2 feet in girth. Bark bright red-brown, 

 broken on the surface into small scales. Young branchlets glabrous. Leaves 

 (Plate 268, Fig. 15) about 3 inches long by 2 inches wide, ovate, broad and rounded 

 at the base, acute or shortly acuminate at the apex; nerves, nine or ten pairs, running 

 parallel and straight to the margin, and ending in acute triangular lobes, which are 

 finely serrate ; upper surface dark green, pubescent on the midrib and nerves ; lower 

 surface yellowish green, glandular, pubescent on the midrib with shght axil-tufts; 

 petioles pubescent, f to i inch long. Buds stalked, pubescent at the base. Stipules 

 deciduous, lanceolate, acute, pubescent. Staminate catkins, three to four, in slender- 

 stemmed racemes ; stamens four. Cones, ovoid-oblong, \ ^o \ inch long, three to 

 four in a raceme ; scales thickened, three-lobed and truncate at the apex ; nutlets 

 nearly circular, surrounded by a thin membranous border. 



This species, distributed over a wide area, shows two well-marked geographical 

 varieties : — 



1. Var. virescens, Callier. This is the commonest form, and has been described 

 above (Plate 268, Fig. 15). 



2. Var. occidentalis, Callier. Alnus occidentalis, Dippel. Leaves (Plate 268, 

 Fig. 14) larger, 4 to 5 inches long and 3 to 4 inches wide; nerves, twelve pairs; 

 slightly bluish-green and pubescent throughout beneath ; stipules ovate, broad, obtuse. 

 This variety is rare, and has only been observed in British Columbia and Oregon. 



This species is widely distributed in western North America. It occurs in 

 British Columbia, from Francis Lake in lat. 61" to the valley of the Lower Fraser 

 River, and extends eastward along the Saskatchewan River to Prince Albert. It 

 extends southwards along the Rocky Mountains to northern New Mexico, and is 

 the common species in the northern interior region, east of the divide of the Cascade 

 Mountains, in eastern Washington, Oregon, Idaho, and Montana. It is very 

 abundant on the southern California Sierra, forming great thickets at 6000 to 7000 

 feet above the sea, along the head- waters of the rivers of southern California flowing 

 to the Pacific Ocean, It is equally abundant and attains its largest size in Colorado 

 and northern New Mexico, and is met with in Nevada and Utah. 



This species is rare in cultivation. There are two or three trees of each variety 

 in the alder collection at Kew, which are about 15 feet in height, and show no 

 special beauty or vigour. Var. virescens is thriving at Aldenham ; and a fine specimen 



