stonewort

Stonewort is the common name for freshwater green algae in the family Characeae, particularly the genera Chara and Nitella. They inhabit clear, still or slow-moving waters in lakes, ponds, and streams, often forming dense underwater meadows on calcareous substrates. The name derives from lime-containing deposits in their cell walls, which give the tissue a hard, stone-like texture when dried.

Description: Stoneworts have a rigid, branching thallus composed of a main axis with whorled branches. The plant body is organized into nodes and internodes, and cells can be very large with a single central vacuole. They contain chlorophyll and store starch. Reproduction is sexual and asexual. In sexual reproduction, male antheridia and female oogonia produce motile sperm that fertilize stationary eggs; many species can spread vegetatively by fragmenting pieces of the thallus.

Ecology: They are important primary producers and provide habitat for invertebrates and juvenile fish. Their calcium carbonate encrustations can contribute to sediment structure. Stoneworts require good light, stable substrates, and relatively low nutrient levels; they are highly sensitive to eutrophication, turbidity, and sedimentation, and their abundance often declines in polluted waters.

Taxonomy and phylogeny: Stoneworts belong to the green algae of the order Charales, division Charophyta (or Streptophyta in some systems). They are among the closest living relatives of land plants and share several anatomical features with bryophytes and tracheophytes.

Distribution and conservation: They are widespread in temperate regions, with species found in North America, Europe, Asia, and parts of Africa and Australia. Because of their sensitivity to water quality, their presence can indicate relatively pristine conditions; declines are commonly used as a bioindicator of eutrophication.

Human uses: In aquaria, some species are kept as aquatic plants, and their presence is often noted as an indicator of water quality.