Cylindrotheca gracilis

This taxon is common in the plankton of large, slow moving rivers, particularly in the eastern rivers of Montana and midwest states. It is, however, greatly under reported because the lightly silicified valves are destroyed in most laboratory processing.

Christensen and Reimer (1968) reported the distribution of C. gracilis in the United States from the following localities: Patuxent River, Prince Georges County, Maryland (brackish water); Ottawa River, Allen County, Ohio (fresh water); Dugout Creek, Dickinson County, Iowa (fresh water). The authors noted that C. gracilis appears to tolerate both fresh and brackish conditions, and that total conductivity, concentration of sulfates, magnesium, calcium, or some combination of these chemical variables may be more critical to the growth and distribution of this diatom than chloride or sodium ions (Christensen and Reimer 1968). Additional records from Idaho, Montana, North Dakota, South Dakota, and Wyoming are found in Bahls (2009) and the Savannah River estuary (Manoylov and Dominy 2013).