202 BETULACEiE. Alnus. 



2. ALNUS, Tourn.; Endl. gen. 1841. alder. 



[Name derived from the Celtic words, aZ, near, and lau, the bank of a river.] 



Sterile fl. Bracts with five bracteoles. Calyx 4-parted. Anthers 2-celled. Fertile fl. 

 Bracts cuneate, truncate, persistent, thick, 2-flowered. Calyx consisting of four scales, 

 which are adnate to the bracts, except at the summit. Fruit compressed, wingless, or 

 rarely with a winged margin. — Trees or shrubs. Fertile amenls ovoid or oblong, paniculate. 



* EnALNUs. Fruit iwt winged, 



1. Alnus serrulata, Willd. (Plate CXV.) Common Alder. 



Leaves obovate, somewhat coriaceous, finely and somewhat doubly denticulate-serrate , the 

 veins underneath and their axils villous; fructiferous aments oblong-ovoid; stipules oval, 

 obtuse ; fruit ovate, not winged. — Willd. sp. 4. p. 336 ; Pursh, fl. 2. p. 623 ; Michx. f. 

 sylv. 1. t. 75. /. 1 ; Bigel. Jl. Bost. p. 342 ; Ell. sk. 2. p. 567; Beck, hot. p. 326 ; Dar- 

 lingt. Jl. Cest. p. 525. A. rubra, Tuckerm. in Sill. jour. 45. p. 33. Betula-Alnus rubra, 

 Marshall, arbust. p. 20. B. serrulata. Ait. Kew. (ed. 1.) 3. p. 338. B.- Alnus serrulata, 

 Michx. jl. 2. p. 181. 



A shrub 6-12 feet high, irregularly branched, and usually growing in dense thickets. 

 Leaves 2-5 inches long, more or less obovate, with a short acumination or obtuse, pro- 

 minently veined, smooth above, paler and sprinkled with resinous dots underneath ; the 

 pubescence of the veins and axils mostly ferruginous : stipules caducous. Sterile aments 

 appearing before the leaves, about two inches long, several together at the extremity of the 

 branches : anthers bright yellow. Fertile aments somewhat paniculate on short naked 

 branches, usually 3-4 together, densely flowered ; in fruit, about half an inch long. Scales 

 of the calyx free at the summit, so that the bracts appear 5-lobed at the apex. Fruit wingless, 

 slightly margined. 



Swamps and wet thickets ; very common. Fl. March - April. Fr. September. 



2. Alnus incana, Willd. Black Alder. 



Leaves thin, ovate or oblong, rather acute, obtuse or somewhat cordate at the base, slightly 

 lobed, acutely serrate, glaucous and pubescent underneath, naked in the axils of the veins ; 

 stipules oblong-lanceolate ; fertile aments oval ; fruit orbicular, not winged. — Willd. sp. 4. 

 p. 385; Hook. Jl. Bor.-Am. 2. p. 157 (in part) ; Tuckerm. I. c. p. 32. A. incana, var. 

 vulgaris, Spach, I. c. p. 206. A. glauca, Michx. f. sylv. 1. t. 75. f. 2. A. crispa, Pursh, 

 Jl. 2. p. 623 (in part). Betula incana, Lirm. suppl. p. 417. 



A shrub 8-20 feet high ; the stem sometimes 3-4 inches in diameter, with a smooth 

 brown bark. Leaves 2-4 inches long, often broadly ovate, pale glaucous green underneath. 



