Jones: Flora of Illinois, 41. Betulaceae 107 



2. Scales of the pistillate catkins 5-lobed, woody, persistent; stamens 4; buds usually 



stalked and with 2 valvate scales; bark not peeling horizontally 2. Altnis 



l.Nuts with a foliaceous involucre or subtended by or enclosed in a large bractlet, 

 borne in clusters or catkins; stamens 3-10; calyx none; buds with several scales. 



3. Shrubs; leaves broadly cordate-ovate, doubly serrate usually with 5-8 pairs of 

 veins; leaf-buds obtuse; nuts in clusters, each enclosed in a foliaceous involucre 

 3. Cor\)lus 



3. Small trees; leaves oval or ovale, with 9 or more pairs of veins; leaf-buds acute; 



fruits in pendent catkins, the nut subtended by or enclosed in a large bractlet. 



4. Fruiting bracts foliaceous, 3-lobed; bark of the trunk and branches smooth; 

 lower surface of leaves glossy green with small tufts of whitish hairs in the 



axils of the principal veins; lateral veins unbranched; anthers glabrous 



4. Carpinus 



4. Fruiting bracts becoming sac-like, inflated, enclosing the nut; bark rough, scaly; 

 lower surface of leaves pale dull green, thinly short-pilose; lateral veins 

 usually forked near the margin; anthers pilose at apex 5. Oslr\^a 



1. Betula L. — Birch 



1. Trees up to 30 m. tall, with acute or acuminate, serrate or double-serrate 



leaves; bark of trunk and large branches pe^Ung horizontally in thin strips. 



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; locally in wooded 



areas in the n. half of III.; known from Lake and Lee counties. Our 



plants have been named var. macrolepis Fern. Yellow Birch 



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 III. May. River Birch B. nigra L. 



2. Bark chalky- or silvery-white; fruiting catkins cylindrical, slender-pedun- 

 cled, usually pendulous, the scales deciduous; wing of the fruit distinct- 

 ly broader than the nutlet; cold woods, local, n. III. May. Paper Birch. 



Canoe Birch B. papyrifera Marsh. 



I. Shrubs 0.5-4 m. tall; bark brown, not exfoliating; twigs of the season 

 pubescent or puberulent, sometimes glandular. 



4. Leaves ovate, acute, 3-6 cm. long, serrate; fruiting catkins 1.5-2.5 cm. long, 



10-12 mm. thick; edge of boggy meadow. Beach, Lake Co., G. N. Jones. 

 [5. glandultfera X lutea Rydb.; B. lutea X pumila var. glandulifera 



Rosend.} X ^- purpusii Schneid. 



4. Leaves obovate, obtuse, or acutish, mostly 1.5-3 cm. long, crenate-dentate; 

 fruiting catkins about 1 cm. long, 6-8 mm. thick; bogs, n.e. III. May. 

 Dwarf Birch B. pumila L. 



2. Alnus Hill— Alder 



1 . Leaves oval to ovate, doubly or coarsely serrate, usually rounded at the 

 base; stipules lanceolate; nut orbicular; wet ground, rare; Lake, McHenry, 

 and Boone counties. June. Speckled Aider A. incana (L.) Moench 



