Salix nigra has the potential to be a large tree, with simple, alternate, toothed leaves. There appears to be a large body of misinformation perpetuating the idea that virtually any large tree willow in Wisconsin is Salix nigra and that it can be identified by its bark alone. In fact, it is far less common than Salix fragilis, an alien species now fully naturalized. Leaves of Salix fragilis are usually glaucous (whitened) beneath and lack stipules, compared to Salix nigra whose leaves are green beneath (not whitened) and often have stipules at the base of the petiole. The willow species are difficult to distinguish and any "shortcuts" around the proven keys are likely to result in frequent errors. See the key to willows for helpful characters to identify the species, or try the more thorough keys in Michigan Flora vol 2.

Salix nigra is near the northwestern limit of its distribution in Wisconsin and is found mostly in the southern part of the state. It becomes established on wet, sunny sites (which may subsequently grow up into forest) and is often associated with streams. It is short-lived, apparently reaching an age of 70-85 years.