Stoneworts (Chara spp., Family Characeae) are a genus of multicellular green algae that superficially resemble regular plants because of the branching stem-like and leaf-like structures. Like higher plants, Chara uses chlorophyll to photosynthesize.

Chara is found in fresh water, particularly in limestone areas throughout the northern temperate zone, where they grow submerged in slow-moving fresh water attached to a muddy bottom.

Chara accumulates lime (calcium carbonate) on the surface of the plant, giving it a rough texture. Over time, the lime can accumulate as extensive calcium carbonate deposits, so extensive that they form the major part of calcareous marls of lakes (i.e., freshwater limestone).