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This is one of the native species of smartweed and somewhat unusual because it is reliably perennial. Mild Waterpepper is a member of a complex of species that are very similar to each other. Other members of this complex include Persicaria opelousana and Persicaria setacea, which are largely restricted to southern Illinois. Some authorities regard these latter two species as variants of Mild Waterpepper rather than distinct species, and there may be some merit to this view. The species Persicaria opelousana has flowers with greenish white tepals and its ochreoleae (small sheaths underneath the flowers) have abundant long bristles (greater than 1 mm. in length). The species Persicaria setacea has leaves that are conspicuously pubescent on both their upper and lower surfaces and its ochreae (sheaths at the base of the petioles) have long hairs and bristles. In contrast, Mild Waterpepper has hairless leaves (or nearly so), only short appressed hairs along its ochreae, and short bristles along the upper rim of its ochreoleae (less than 1 mm. in length). It is also possible to confuse Mild Waterpepper with Persicaria punctata (Dotted Smartweed) and Persicaria hydropiper (Waterpepper). Dotted Smartweed has glandular dots on its tepals (which may be difficult to see) and its mature leaves are more widely spaced along the stems (about 1–3½' apart). Waterpepper has ochreoleae that lack bristles and it has more widely spaced flowers on nodding racemes. The leaves of both Dotted Smartweed and Waterpepper have a more peppery flavor than those of Mild Waterpepper. Another scientific name that refers to Mild Waterpepper is Polygonum hydropiperoides.