P. monilífera.
6. Pópulus monilífera, Ait. (Cottonwood. Carolina Poplar. Necklace-poplar.) Leaves large, broadly heart-shaped or deltoid, serrate with cartilaginous, incurved, slightly hairy teeth. The rapid-growing young twigs very angular and bearing very large (6 to 9 in. long) leaves. A very large (80 to 100 ft. high) tree, common in the Mississippi valley, but found in western New England and often planted.
P. nìgra.
7. Pópulus nìgra, L. (Black Poplar.) Leaves rather large, deltoid, pointed, serrate with glandular teeth, smooth on both sides even when young. Leafstalk somewhat compressed. Buds very sticky. A very variable, large (50 to 80 ft. high), rapidly growing tree with spreading branches. Occasionally planted. From Europe.
P. balsamífera.
8. Pópulus balsamífera, L. (Balsam-poplar. Tacamahac. Balm of Gilead.) Leaves very large, ovate, gradually acuminate, sometimes heart-shaped, finely serrate, smooth, bright green and shining on both sides; leafstalk nearly round; leaves in spring rich yellow. Branches ridged below the leaves; buds large and covered with very fragrant resin. A medium-sized tree, 40 to 70 ft. high, pyramidal in form. Wild in the North and often cultivated.
Var. candicans, or Balm of Gilead, has larger and more or less heart-shaped leaves (the larger figure in the cut).