This subaquatic perennial, circumboreal species is widespread in cool temperate regions of North America. It is easily confused with the more weedy anagallis-aquatica (or glandifera), and combined by some authors (K). Sterile hybrids may be expected (Cr; Clapham et al. 1962). Based on Pennell (1935; see also F and Cr), catenata has obtuse to acute sepals (versus acute to acuminate); capsules relatively broad (reniform-obcordate versus ovate-orbicular) and more distinctly notched; and leaves more elongated (with L/W ca. 3-5 versus 1.5-3). Other authors (Clapham et al. 1962; J, W) have emphasized its smaller racemes (5-35 versus 20-65) with shorter pedicels (3-6 mm versus 4-8 mm). Two old colls. from Ky. are confirmed here: from FAYE (KY-Agr., PH; J.S. Terrill, 23 Jul 1892; Pennell 1935) and OLDH (DHL; M. Seargent #51). These colls. are referable to var. glandulosa (Farw.) Pennell, the predominant form in eastern regions (F). Two colls. from FRAN have also been reported (SERNEC 2023); these need to be examined.