There has been unsettled nomenclature within section Longifoliae, which is a largely western group that has the following characters: deciduous pistillate bracts, leaves that have stomata on both surfaces, relatively elongated shape and remote serrations; and usually extensive clonal root-sprouts (FNA 7). S. interior occurs mostly in midwestern and northeastern regions but it extends locally into the Interior Low Plateaus on calcareous soils; it is absent from the southeastern Coastal Plain except in Miss. (K). .In Ky. it is most common along larger rivers and it has spread locally into artificial ponds west of the Appalachians. Plants here have sometimes been treated as the eastern segregate of a more widespread species: S. exigua Nutt. var. sericans (Nees) Nesom. Hybrids can be expected with other species, including eriocephala; such plants are largely sterile but potentially vigorous (FNA 7). Some relatively short shrubby plants along smaller rocky streams in the Bluegrass region (with colls. from ANDE, CAMP, CASE, HARR, FAYE, FRAN, JEFF, NICH, OWEN, TRIM and elsewhere) have leaves that tend to be smaller (mostly 5-10 mm wide versus 7-12 mm), more persistently sericeous, and deeper bluish-green. These plants form less open clonal patches, and they may root less readily from cuttings, compared to typical interior. They have sometimes been named var. wheeleri Rowlee in Ky., but that largely midwestern taxon has not been generally recognized (F, Argus 1986, FNA 7). Schaffner (1914) and others have applied the name wheeleri to plants on seasonally dry sites among sand dunes in n. Ohio, n. Ind, and s. Mich., but he noted there was gradation into typical plans on wetter sites. Further investigation is needed; it is possible that increased pubescence is sometimes induced by herbivory or stress in some species of Salix (Dalin et al. 2008).