3a. Leaves thick, coarsely and doubly serrate, broadest near the 



middle (Elm) 4. 



3b. Leaves thin, simply serrate, broadest distinctly below the mid- 

 dle Hackberry, Celtis occidentals. 

 4a. Some of the branches with flat corky wings; leaves smooth 

 above Cork Elm, Ulnius racemosa. 

 4b. Branches without corky wings; leaves more or less rough 

 above 5. 



5a. Petioles and axillary buds glabrous. White Elm, Ulmus americana. 

 5b. Petioles and axillary buds pubescent with rusty hairs 



Slippery Elm, Ulmus fulva. 



6a. Leaves rough above Red Mulberry, Morus rubra. 



6b. Leaves smooth above White Mulberry, Morus alba. 



7a. Leaves alternate 8. 

 7b. Leaves opposite 9. 



8a. Leaves 2 5 cm. long, stems pubescent 



Pellitory, Parietaria pennsylvanica. 

 8b. Leaves 8 20 cm. long; stem armed with stinging hairs 



W r ood Nettle, Laportea canadensis. 



9a. Twining plant; leaves serrate or cleft Hop, Humulus lupulus. 

 9b. Erect plant; leaves palnlately compound Hemp, Cannabis sativa. 

 9c. Erect plants; leaves not lobed or compound 10. 



lOa. Stems armed with stinging hairs 11. 



lOb. Stems glabrous or rough, but not with stinging hairs 12. 



lla. Leaves ovate, with a heart-shape base 



Stinging Nettle, Urtica dioica, 



lib. Leaves lanceolate or ovate-lanceolate, not heart-shape at base 



Slender Nettle, Urtica gracilis. 



12a. Stems glabrous, pellucid Clearweed, Pilea pumila, 



12b. Stems rough, opaque False Nettle, Boehmeria cylindrica. 



SANTALACEAE, the Sandalwood Family 



Low herbs with alternate entire leaves and terminal clusters of 

 small greenish-white bell-shape flowers without petals in spring and 

 early summer. 



la. Inflorescence of several-flowered clusters terminating the stem 

 and in the upper axils Toad-flax, Comandra umbellata. 



Ib. Inflorescence of axillary clusters of 1 5 flowers 



Toad-flax, Comandra livida. 



