Audouinella

Audouinella is a wide-spread genus of red algae, found in marine and freshwater. Grows as small tufts of red, brown, or black hairlike filaments on any solid surface - most dramatically on the edges of slow-growing leaves. Often tolerant of high levels of pollution, acidity, and thrives on dissolved phosphate and nitrates. Reproduces via spores.

The form known as Black Brush Algae is a particular nuisance in aquaria as few fish, even those widely promoted as algivores, will eat it.