Ranunculus cardiophyllus is quite variable. Through most of its range, leaves always have rounded marginal crenae and cordate or truncate bases, stems are often densely pilose (but may be sparsely pilose or glabrous), and achene beaks are curved. In plants from Arizona and New Mexico, however, leaves may have obtuse marginal crenae or broadly obtuse bases, stems are never densely pilose, and achene beaks are sometimes straight. Forms showing some or all of these charactersistics are often separated as R . cardiophyllus var. subsagittatus . The characteristics are poorly correlated, however, and taxonomic recognition is not warranted.
Most specimens of Ranunculus cardiophyllus have all of the basal leaves unlobed, but plants with the innermost basal leaf 3-5-lobed are common. A few specimens, mostly from the northern part of its range, have all of the basal leaves 5-parted or -divided. Those plants approach R . pedatifidus in their morphology, and R . cardiophyllus has sometimes been considered a variety of that species.
