KEY TO THE GENERA 13 



(y) Leaflets lobed or doubly serrate Acer: boxelder 219 



y. Leaves alternate 

 (x) Leaflets entire 

 m. Leaflets elliptic, small; thorny Robinia: locust 175 



n. Leaflets ovate, large; thornless Ailanthus: tree-of-heaven 83 



(y) Leaflets at least finely serrate 

 m. Large tree ; fruit a nut 



(m) Pith in plates; leaflets 11-23 Juglans: walnut, butternut 232 



(n) Pith solid; leaflets 5-11 Carya : hickory 238 



n. Small trees ; fruit fleshy, bright red 



(m) Sap milky Rhus: sumac 227 



(n) Sap not milky Sorbus : mountain ash 147 



2. Shrubs or vines 



a. Leaves evergreen and leathery 



(1) Creeping or prostrate shrubs 



(a) Leaves narrowly linear, thick, edges folded 



back Empetrum : crowberry 105 



(b) Leaves lanceolate to rounded, rarely linear , 

 x. Leaves less than 12 mm. long 



(x) Leaves much longer than wide Vaccinium: cranberry 97 



(y) Leaves broadly ovate Chiogenes : snowberry 95 



y. Leaves regularly more than 12 mm. long 



(x) Leaves serrate, fragrant Gaultheria : ivinter green 93 



(y) Leaves entire, not fragrant 

 m. Leaves narrowed at base 



(m) Leaves scarcely 12 mm. long, pale 



and resinous below Vaccinium: mountain cranberry 102 



(n) Leaves 12-25 mm. long, green and 



veined below Arctostaphylos: bearberry 94 



n. Leaf base not narrowed ; leaf broadly 



elliptic Epigaea : trailing arbutus 90 



(2) Erect shrubs 



(a) Leaves entire, with revolute margins 



x. Leaves woolly below Ledum : Labrador tea 87 



y. Leaves smooth and white below 



(x) Leaves opposite or in threes Kalmia: swamp laurel 89 



(y) Leaves alternate Andromeda : moorwort 92 



(b) Leaves toothed 



x. Plant distinctly woody, leaves finely toothed Chamaedaphne : leatherleaf 91 



y. Plant semiherbaceous, leaves coarsely toothed Chimaphila : pipsissewa 86 



b. Leaves deciduous 

 (1) Leaves simple 



(a) Leaves not lobed on mature twigs 

 x. Leaves opposite or in whorls 

 (x) Leaves entire 

 m. Leaves silvery-scurfy Shepherdia: buffalo berry 211 



n. Leaves green 



(m) Stipules present, leaves often in 



threes Cephalanthus : button-bush 276 



(n) Stipules absent, leaves in pairs 

 r. Leaf-scars running together to form 

 a ring 

 (r) Stems hollow 

 h. Low shrub, 0.3-1 m. high Symphoricarpus: wolf-berry 284 



i. Tall shrubs or vines, over 1 m. 



high Lonicera : honeysuckle 286 



(s) Stems solid 

 h. Flowers and fruit axillary, in 

 pairs, leaves very short peti- 



oled Lonicera : honeysuckle 286 



i. Flowers and fruit in terminal 



