stoneworts

Stoneworts, or Charales, are a group of freshwater green algae in the family Characeae. They are among the more morphologically advanced algae and are considered one of the closest living relatives to land plants. Stoneworts form dense underwater stands in clear, calm waters such as lakes, ponds, and slow-moving rivers.

Their thalli resemble small aquatic plants, with a main axis bearing whorled or branched limbs. The tissues often contain deposits of calcium carbonate in the walls, giving the thallus a stony or limestone-like texture. They attach to the substrate by rhizoids and can form tufted, intricate structures that create habitat complexity for other aquatic organisms.

Stoneworts reproduce sexually through oogamy. Sperm produced in antheridia swim to eggs in archegonia when water is present, fertilizing them to form a zygote. The zygote then gives rise to a sporophyte, typically a dependent stage that remains associated with the parent. Asexual reproduction by fragmentation of the thallus is also common, enabling rapid spread in suitable conditions.

Ecology and significance: Stoneworts contribute to underwater habitat complexity, providing shelter and foraging surfaces for invertebrates and fish, and they can influence sediment stabilization and oxygen dynamics. They are sensitive to nutrient pollution and turbidity, so their presence often indicates good water quality. They are of interest in paleobotany and ecology because their calcified structures preserve well in the fossil record and reflect ancient freshwater environments.

Taxonomy: Stoneworts include genera such as Chara and Nitella, forming the order Charales within the green algae.