Gratiola Linnaeus. Hedge-hyssop.
A genus of about 20 species, herbs, of temperate regions (and tropical mountains) of the Old and New Worlds. Circumscription of the genus includes Amphianthus (following Estes & Small 2007, 2008).
ID notes: Gratiola amphiantha somewhat resembles Callitriche, but has floating leaves in single pairs rather than in a whorl.
Ref: Estes & Small (2007); Estes & Small (2008); Freeman (2019b) In Flora of North America Editorial Committee (2019); Pennell (1935). Show full citations.