Stoneworts are a special type of algae that like seaweeds have a complex structure with stems and branches. They are submerged freshwater plants that are called stoneworts because they are often encrusted with calcium deposits, giving them a rather brittle feel when handled. They prefer to grow in clear, mineral-rich unpolluted water in still water and because of a loss of this type of habitat, many are now very rare.

We have one species currently recorded on the Fen, Chara vulgaris, which has formed some good patches in zone 3.

Chara vulgaris is known from Hampshire although it is not very common. This is an extract from the BSBI distribution map. Clausentum fen is the dark red square over Winchester.

Below are some more photographs taken from material collected on the Fen, showing the magnified structure of Chara.


The elongated stems consist of straight parts called internodes, with branchlets forming at the nodes.

A developing branchlet

Stipuloides and spines are important features that help in the identification of stonewort species.

Sexual organs are found at the base of the branchlets. These are male antheridia which release the male sex cells into the water.