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CommentsHeart-Leaved Willow has an unstable taxonomic history and some authorities regard it as a variation of another species, Salix eriocephala (Missouri River Willow). Following Mohlenbrock (2002), this willow is considered a distinct species, Salix rigida. Generally, Heart-Leaved Willow differs from the Missouri River Willow by always remaining a shrub (12' or less) and having leaves that are slightly more wide. Furthermore, it often has woody stems that are yellowish tan, instead of reddish brown. Heart-Leaved Willow is also closely related to another shrubby willow, Salix glaucophylloides (Blue-Leaf Willow). Blue-Leaf Willow has leaves that are slightly more wide and more coarsely toothed than those of Heart-Leaved Willow, but these differences are not dramatic. Occasionally these and other willows hybridize, making identification even more difficult than it already is. Heart-Leaved Willow has been referred to as Salix cordata in the past, but this scientific name refers to another willow species further to the east that has much hairier stems and leaves.