Water feather-foil : The water violet (Hottonia palustris); also, the less showy American plant H. inflata.

Example:


Taxonomy
bay, Delmarva, Feather, Foil, Plants, Photograph, Natural Heritage Program, Hottonia, freshwater wetlands, rare plants, plants and animals, R. Harrison, Wiegand, Katharine, McCarthy, Maryland's Eastern Shore, standing water, winter and spring.

Defination from the web:
Feather Foil. Featherfoil, Hottonia inflate. Photograph by R. Harrison Wiegand. Delmarva Bay. Photograph by ... They are sensitive to disturbances which alter underground water supplies. Ditching and draining have destroyed many bays and few good examples of these wetlands remain. ...