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| Stoneworts | ||||||||||
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 Chara fragilis | ||||||||||
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The Charales are in the division Charophyta. They are green plants believed to be the closest relatives of the green land plants. Linnaeus established the genus (Chara) in 1753. They have large, macroscopic, thalli growing up to 120cm long, they are branched, multicellular, and use chlorophyll to photosynthesize. They grow in fresh water. They may be called stoneworts, because the plants can become encrusted in lime (calcium carbonate) after some time. The "stem" is actually a central stalk consisting of giant, multinucleated cells. They are unique in having a whorl of small branchlets at each node in the stipe, this gives them a superficial resemblance to the genus Equisetum. In these whorls it is possible to see the phenomenon of cytoplasmic streaming very well. In fact the streaming in Chara is the fastest recorded of any cell. Cytoplasmic streaming is caused by the microfilaments found inside the cell, as proven by the use of cytochalasin B to stop streaming.
There are about 400 species world-wide, with 33 in Britain and Ireland according to Groves and Bullock-Webster),Groves, J. and Bullock-Webster, G.R. 1920. The British Charophyta. Vol.1, Nitelleae. London, The Ray SocietyGroves, J. and Bullock-Webster, G.R. 1924. The British Charophyta. Vol.2, Characeae.. London, The Ray Society however (Stewart and Church (1992) reduce this to 21.Stewart, N.F. and Church, J.M. 1992. Red Data Books of Britain and Ireland. The Joint Nature Conservation Committee, Peterborough. ISBN 1 873701 24 1
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Submerse meadow of Chara spec.
Limy crust on Chara spec. in a spring pond
The Characeae are aquatic and some can survive in brackish or maritime habitats. They are to be found usually in still, non-flowing, water attached by rhizoids. They can be pioneer colonizers or ephemerals.John, D.M., Whitton, B.A. and Brook, A.J. 2002. The Freshwater Algal Flora of the British Isles. Cambridge University Press, London. ISBN 0 521 77051 3
The antheridia and oogonia are protected by a layer of sterile cells when mature; the oogonium is oblong in shape and consists of a single egg, while the spherical antheridium is packed with threadlike cells that produce spermatia. As a result, the Charales have the most complex structure of all green algae, if indeed they should be so labelled.
The possible ancestors of the land plants are also known as brittleworts or skunkweed. These curious labels arise from the fragility of their lime-encrusted stems, and from the foul odor these produce when stepped on.
Many botanists propose that the stoneworts and their relatives be placed in a phylum, division, sub-kingdom, or even kingdom by themselves, often named Charophyta. Their classification by taxonomists is currently undergoing much cladistic scrutiny. Further DNA and RNA analysis may prove the charophytes to be a crucial evolutionary link in the phylogenetic tree of life, the critical developmental step from the algae toward the non-vascular and then vascular land plants.
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