22 American Midland Naturalist Monograph No. 4 



Capsules thickish, narrowly egg-shaped to roundish; in the Southwest. 

 Fruit-stalks shorter than the capsules; in Zion and Grand Canyon 



National Parks Fremont Cottonwood (P. Fremonli). 



Fruit-stalks 2 to 3 times longer than capsules ; in Mesa Verde 



and Bryce Canyon National Parks 



Valley cct'.onwood (P. IV islizeni) . 



Leaf-stalks round, the blades usually lancc-shaped to narrowly egg-shaped 

 (rarely heart-shaped in balsam p>oplar). 



Leaves lance-shaped, green on both sides; in Rocky Mountains and in 



Zion and Bryce Canyon National Parks 



Narrowleaf cottonwood (P. angustifolia) . 



Leaves mostly broadly lance-shaped to narrowly egg-shaped, occasion- 

 ally broader or sometimes heart-shaped, dark green above, 

 whitish below. 



Capsules hairy; lower elevations in Pacific slope parks 



Black cottonwood (P. irichocarpa) . 



Capsules smooth; in Rocky Mountains and on Isle Royale 



Balsam poplar (P. balsamifera) . 



Leaves commonly narrow, mostly lance-shaped, sometimes egg-shaped, rarely 



roundish; scales of catkins not lobed nor toothed SALIX. 



Scales of catkins yellowish, soon falling; stamens 3 or more, the filaments 

 hairy below ; leaves smooth on both sides. 



Leaves green on both sides, mostly lance-shaped; stamens 3 to 5 



Narrowleaf black willow (5. Cooddingi). 



Leaves pale or whitish below, lance-shaped to egg-shaped. 



Leaf-stalks glandular; widespread in the parks 



Western black willow (5. lasiandra and vars.). 



Leaf-stalks not glandular; in Yosemite and Zion National Parks 



Red willow (5. laevigala). 



Scales of catkins dark brown, persistent; stamens 2, the filaments smooth; 

 leaves dark green above, whitish and hairy below. 



Leaves mostly lance-shaped; filaments mostly united below; capsules 



smooth Arroyo willow (5. lasiolepts). 



Leaves elliptic with somewhat broader tips; filaments distinct; cap- 

 sules finely hairy; widespread in the western parks 



- Fire willow (5. Scouleriana) . 



Fruits small more or less winged nutlets, the scales foiming small cones BETULACEAE. 



Cones somewhat woody, borne in clusters of several, not falling to pieces on 



tree ; Pacific species ALNUS. 



Leaves rather coarsely toothed, the margins inrolled; older bark whitish or 



grayish; in the Northwest Red alder (A. rubra). 



Leaves finely toothed, the margins flat; older bark brown and scaly; in 



Sierra Nevada White alder (A. rhombifoUa) . 



Cones composed of papery scales, borne singly, falling to pieces on tree; found 



mostly east of Pacific slope BETULA. 



Cones cylindric, spreading or pendent on slender stalks; wing broader than 

 the seed-like nutlet. 



Bark whitish, separating into thin layers; northern species 



Paper birch (B. papyrifera). 



Bark reddish-brown, not separating into layers; widespread species 



Red birch {B. fontinalis). 



Cones oblong-egg-shaped, borne erect without stalks; wing not broader than 

 the seed-like nutlet; eastern species. 



