T r e e s  o f  N o r t h  C a r o l i n a

Populus L. (Salicaceae)

A genus of about thirty-five species of trees; largely north temperate.

Ten species occur in North Carolina, but only four are native to the state.

Key to Populus in North Carolina

1. Winter buds not viscid; stamens 5-20...2.

2. Stamens 12-20; scales of the catkins deeply fimbriate; petioles terete...P. heterophylla (Swamp cottonwood)

2. Stamens 5-12; scales of the catkins dentate or with only 3-7 linear-trianglar lobes; petioles strongly flattened laterally (90 degrees to the plane of the leaf blade), especially near the junction with the blade...3.

3. Petioles strongly flattened laterally; leaves glabrous when mature (pubescent when young in P. grandidentata); [native trees]...4.

4. Leaf margins coarsely crenate- or undulate-toothed, with fewer than 12 (-15) teeth per side, the sinuses of the larger teeth 1.5-6 mm deep; leaves puberulent beneath when young (glabrate in age); buds gray-pubescent...P. grandidentata (Bigtooth aspen)

4. Leaf margins finely crenulate-serrulate, with 15-35 (-70) teeth per side, the sinuses 0.5-1.0 mm deep; leaves glabrous; buds glossy brown...P. tremuloides (Quaking aspen)

3. Petioles terete or nearly so; leaves densely pubescent (P. alba) or glabrescent (P. x canescens); [exotic trees]...5.

5. Leaves of vigorous shoots palmately 3-7-lobed (and also toothed); leaves densely white-tomentose beneath when young and mature...*P. alba (Silver poplar)

5. Leaves of vigorous shoots merely toothed; leaves glabrescent when mature...*P. x canescens (Gray poplar)

1. Winter buds viscid (sticky and shiny as if recently varnished); stamens (15-) 20-80...6.

6. Petiole terete or dorsally flattened (in the plane of the leaf blade), and often also channeled above; leaf blades dark green above, glaucous white beneath; leaf margin not translucent, finely serrate with teeth < 1 mm deep...*P. simonii (Chinese poplar)

6. Petiole laterally flattened (90 degrees to the plane of the leaf blade), especially near the junction with the blade; leaf blades light green above, often paler beneath but not distinctly whitened; leaf margin translucent, finely to coarsely serrate with teeth > 1 mm deep...7.

7. First-year branches reddish-brown; leaves noticeably paler beneath; flattened portion of petiole < 2x as deep as wide; early leaves with > 20 teeth per side, the largest < 2.5 mm deep...*P. x jackii (Balm-of-Gilead)

7. First-year branches yellow- to orange- brown; leaves nearly the same color above and below; flattened portion of petiole > 2x as deep as wide; early leaves usually with < 20 teeth per side, the largest < 2.5 mm deep...8.

8. Stigmas 3-4; stamens (30-) 40-80; [native tree, common]...P. deltoides ssp. deltoides (Eastern cottonwood)

8. Stigmas 2-3; stamens (15-) 20-30; [alien trees, rare out of cultivation]...9.

9. Floral disk 2-4 mm wide; stigmas 2-3; ovules and seeds 6-14 (-20) per placenta...*P. x canadensis (Hybrid black poplar)

9. Floral disk 1-2 mm wide; stigmas 2; ovules and seeds 4-8 per placenta...*P. nigra (Black poplar)