River banks and also roadsides, not common.

Sometimes there is a second poorly developed (or rarely fully developed) grain on one of the inner tepals. One collection, from Cheboygan Co. (F. C. Gates 10533, F, MO), even has grains on all 3 tepals. Such specimens and those too immature to show clearly that only one of the inner tepals is forming a well developed grain can usually be distinguished from R. triangulivalvis, which also has flat entire leaves with axillary shoots, by the more ovate-lanceolate leaf blades (ca. 4–5 times as long as wide, or broader). The mature fruiting perianth is ca. 4–5 (–6) mm long; in R. triangulivalvis it is ca. 3–3.5 (–4) mm long.