66. Betulaceae 149 



serrate leaves; bark of tniiik and large branches peeling hori- 

 zontally in thin strips. 

 2. Bark chalky- or silv'ery-white; iriiiting catkins cylindrical, 



slender-peduncled, usually pendulous, the scales deciduous; 



wing of the fruit distinctly broader than nutlet; cold woods, 



local; Carroll, Cook, Jo Daviess, and Lake counties. May. 



Paper Birch. Canoe Birch B. papyrijera Marsh. 



2. Bark of trunk gray or brown; fruiting catkins erect or suberect, 



the scales more or less persistent; wing of the fruit not broader 



than the nutlet. 



3. Fruiting catkins nearly sessile, ovoid or subglobose; bracts 



ciliate; leaves oval; bark of twigs with faint wintergreen 



flavor; wooded areas in the n. half of 111.; known from 



Du Page, Lake, Lee, Ogle, and Winnebago counties. 



Yellow Birch. [B. lutea var. macrolepis Fern.] 



B. lutea Michx.f. 



3. Fruiting catkins short-peduncled, ellipsoid; bracts tomentose; 

 leaves rhombic-ovate; bark bitter, not aromatic; river 

 banks; the common birch in 111.; chiefly in w. and s. 111.; 



also Kankakee Co. May. River Birch B. nigra L. 



1. Shrubs 0.5-6 m tall; bark brown, not exfoliating; twigs of the 



season pubescent or puberulent, sometimes glandular. 



4. Leaves ovate, acute, 3-6 cm long, serrate ; boggy meadows ; Volo 

 and Waukegan, Lake Co., G. N. Jones. [B. glandulifera X 

 lutea Rydb. ; B. lutea X pumila var. glandulifera Rosend.] 

 B. purpusii Schneid. 



4. Leaves obovate to suborbicular, obtuse, or acutish, mostly 1.5-3 

 cm long, crenate-dentate; twigs without glands; bogs, north- 

 eastern 111., in Boone, Cook, Lake, McHenry, and Winnebago 

 counties. May. Dwarf Birch. [B. pumila var. glandulifera 

 Regel, with leaves glandular-resiniferous, usually on both 

 sides, and the two-year-old twigs with scattered glands, has 

 been collected in Lake Co. {A. Chase, E. J. Hill, G. N. 



Jones), and Winnebago Co. {E. W. & G. B. Fell)] 



B. pumila L. 



2. Ahius B.Ehrh. — Alder 

 L Leaves with 9-12 veins on each side of midrib; shrubs. 



2. Leaves oval to ovate, doubly or coarsely serrate, usually rounded 

 at the base; stipules lanceolate; nut orbicular; wet ground, 

 rare; Boone, Cook, Lake, McHenry, and \\'innebago counties. 



June. Speckled Alder. [A. incana sensu auth.] 



A. rugosa (DuRoi) Spreng. 



2. Leaves obovate, finely serrate, tapering at the base; stipules 

 oval; nut ovate; wet ground, s. 111. Apr.-May. Smooth Alder. 

 [A. rugosa sensu auth., non Spreng.] ....A. serrulata (Ait.) Willd. 



