Plants to 35 m, 14 dm diam.; strongly heterophyllous. Bark dark grayish brown, furrowed only basally on large trees, (light gray and smooth otherwise). Branchlets reddish brown, becoming reddish gray by third year, round, 1.3-2.5 (-5) mm diam., moderately coarse, thinly tomentose to glabrate. Winter buds reddish, proximally pubescent, (dull), not evidently resinous; terminal buds 2.5-7 (-10) mm, (glabrous or pubescent); flowering buds separated on branchlets or clustered distally, 6-9(-13) mm. Leaves: petiole distally flattened at right angle to plane of blade, 1.5-6(-11) cm, 1/2-3/4 blade length; blade ovate, (2-)4-10(-27.5) × (2-)3-8(-28.5) cm, w/l = 3/4, base broadly cuneate to subcordate, basilaminar glands (1 or) 2(-4), cup-shaped, margins not translucent, not ciliate, apex acute, abaxial surface greenish-white, resin stains absent, (glaucous), densely silky, (hairs white, relatively long, appressed) at emergence, soon becoming glabrate, adaxial bright dark green, glabrous; preformed blade margins coarsely serrate midblade, teeth (1-)5-12 (-16) on each side (graded, sharp), sinuses 0.3-4.5(-6) mm deep; neoformed blade margins finely crenate-serrate throughout, teeth (5-)15-50(-138) on each side (rounded), sinuses 0.8-1.5(-2.5) mm deep. Catkins densely (30-)50-150(-175)-flowered, (4-)6-10(-14 in fruit) cm; floral bract apex deeply cut, ciliate. Pedicels 0.2-1.5(-2 in fruit) mm. Flowers: discs narrowly cup-shaped, obviously oblique, shallowly toothed, 1-2 mm diam.; stamens 6-12; anthers truncate; ovary 2-carpelled; stigmas 2, filiform, erect. Capsules narrowly ovoid, 2-5(-6) mm, glabrous, 2-valved. Seeds (3-)6-8(-9) per placenta. 2n = 38. Flowering Mar-May; fruiting May-Jun. Dry to moist, open to closed upland woodlands and forests; 0-1000 m; Man., N.B., N.S., Ont., P.E.I., Que.; Conn., Del., D.C., Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., Tenn., Vt., Va., W.Va., Wis. Populus grandidentata is a successional species that regenerates after fires by suckering from living rootstocks. The exclusively neoformed leaves on such suckers are much larger than those found on mature trees, are conspicuously pubescent abaxially, and are similar enough to preformed and neoformed leaves of P. heterophylla that they are responsible for incorrect published reports of the latter in upland sites. Once suckers reach their second or third year and begin to branch, they start to bear at least some preformed leaves that clearly identify them as Bigtooth aspen. As far as is known, P. grandidentata and P. heterophylla never grow together at a single site.

Bigtooth aspen hybridizes sporadically with the other native aspen, Populus tremuloides, to form P. ×smithii B. Boivin (synonym P. ×barnesii W. H. Wagner) throughout their large region of sympatry (Frère Marie-Victorin 1930; S. S. Pauley 1956; B. V. Barnes 1961; W. H. Wagner Jr. 1970). Leaves of the hybrids have more numerous, smaller, more rounded teeth than those of P. grandidentata. They may be found as far west as Niobrara River valley, Nebraska, 350 km west of the nearest present station of P. grandidentata.

The related Eurasian white poplar, Populus alba Linnaeus, is commonly and widely planted throughout temperate North America as a pistillate clone with a spreading crown or, less often, as a columnar staminate clone, the Bolleana poplar (`Pyramidalis´), both of which can persist after cultivation and even spread to a limited extent by root sprouts in old garden sites, roadsides, waste places, hedgerows, and edges of woods. This species differs from P. grandidentata (and all other species of the genus) in having neoformed leaf blades palmately 5-lobed and, along with the petioles, densely white-tomentose abaxially. Unlike all native species of Populus, white poplar has floral bract apices only shallowly cut; these are ciliate like those of native aspens. Populus alba hybridizes commonly with both P. grandidentata, forming P. ×rouleauiana B. Boivin, and P. tremuloides, forming P. ×heimburgeri B. Boivin, in southeastern Canada and the northeastern United States; the hybrids are progressively uncommon southward (E. L. Little Jr. et al. 1957; T. A. Spies and B. V. Barnes 1982). Although their leaves are tomentose abaxially, they differ from