Charales

The Charales are an order of green algae, and are believed to be the closest relatives of the embryophyte plants. They are branched, multicellular green algae that grow in fresh water. They are often called stoneworts, because the plants can become encrusted in lime (calcium carbonate) after some time. They are unique in having a whorl of small branchlets at each node in the stem. Its antheridia and oogonia are protected by a layer of sterile cells when mature, and have the most complex structure of all green algae.