4. Didiplis Raf. (water purslane)

One species, eastern and central U.S.

Didiplis traditionally was included in the genus Peplis L. (Steyermark, 1963; Graham, 1964) along with seven other European species. These other species all have relatively reduced flowers lacking petals (or with small petals that are shed early) and have been determined to be closely related to Lythrum (D. A. Webb, 1967; Graham, 1975; Graham et al., 2005). The relationships of Didplis to other genera requires further study, but may be closest to Rotala L. (Graham et al., 2005; J. A. Morris, 2007).