In its broad definition, this is a widespread variable, frequently hybridizing species of northeastern and midwestern regions, plus a large disjunct population centered in Ala. (Dorn 1995; FNA 8, W). It is known from several types of habitat; segregates may occur; and nomenclature has been confused. Most plants in eastern U.S.A. and adjacent Canada are referable to var. eriocephala, including S. rigida (Muhl.) Andersson (but not including S. cordata Muhl. non Michx.). In Ky. it mostly occurs on cobble bars along medium-sized streambanks, especially streams lined with loose calcareous rocks in the northern Bluegrass region. It is locally common along lower Benson Cr. (FRAN) and Fork Lick Cr. (PEND). At Benson Cr. there may be hybrids with interior, caroliniana and nigra. S. eriocephala is closely related to sericea and occasional hybrids are known, as exemplified by colls. from MENI (DHL see Argus 1986) and perhaps HARD (JC from Stephensburg Lake); see notes on diagnostic characters in FNA 7. However, habitats do not usually overlap in Ky. Leaves of eriocephala are similar to those of caroliniana, but tend to be less strongly glaucous below, to dry more blackish above (versus olive), and have longer petioles (ca. 5-14 mm versus 3-7 mm), which lack distinct glandular processes at summit (as often present in sections Protitea and Salix). Stipules tend to be more developed, semi-ovate to subreniform and acutish (versus broadly reniform and obtuse). Large leaves on vigorous non-flowering shoots are often distinctly cordate. Also, buds and twigs are distinctly reddish (versus more yellowish). In Ky., this species tends to retain green leaves later than others in the genus, sometimes into late Nov or even early Dec (cultivated in 2018).