In its broad sense, this southeastern riparian willow has a somewhat fragmented range, occurring mostly on the western side of the Appalachians and Interior Low Plateaus, in the Ozark-Ouachita region, and on the south Atlantic Coastal Plain (FNA 7, K). Deeper analysis of variation is needed; the more southern plants appear distinct, with more elongated leaves. Some of these southern plants led Small (1933) to establish the name S. amphibia for them; but many of them have suggested hybrid origin from caroliniana sensu stricto and nigra (FNA 7). In Ky. caroliniana is widespread on rocky banks or cobble-bars along larger streams and rivers, but it is generally absent along smaller streams, where replaced by sericea (on acid soils) or eriocephala (on base-rich). S. caroliniana has the most strongly glaucous lower leaf surfaces among native willows of Ky., but see also notes under eriocephala, which can be confused based on this character; glaucousness varies much in both species. S. caroliniana often lacks distinctly brittle branches, as found in nigra. Clear hybrids with nigra appear to be widespread in Atlantic states, but have not been documented in the Ohio Valley or central Mississippi Valley (Argus 1986; Y). In east-central states, caroliniana appears to flower 2-4 weeks later than nigra and other congeners, usually in late April to early May (F; and pers. obs.); this delay may be related to the danger of late spring flooding along the rivers where it grows. Variation across the range of this species deserves deeper study. Plants on the Coastal Plain often become relatively large (up to 5-10 m tall versus 3-5 m inland), and they tend to have longer leaves, with relatively broad bases and more acuminate apices.