Charales

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Stoneworts

Scientific classification

Kingdom:	Plantae
Division:	Charophyta
Class:	Charophyceae
Order:	Charales
Family:	Characeae

Genera

Chara
Lamprothamnium
Nitella
Tolypella

The Charales are an order of green alga, plants believed to be the closest relatives of the green land plants. They are branched, multicellular, chlorophyll-using plants that grow in fresh water. They are often 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. In these whorls it is possible to see the phenomena 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. Its 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.

These 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 seaweeds toward the non-vascular and then vascular land plants.

[edit] References

Groves, J., and Bullock-Webster, G.R. 1920. The Charophyta. Vol.1. Nitellae. London, The Ray Society.

Groves, J., and Bullock-Webster, G.R. 1924. The British Charophyta. Vol.2, Characeae. London, The Ray Society.

John, D.M., Whitton, B.A. and Brook, A.J. (Editors) 2002. The Freshwater Algal Flora of the British Isles. Cambridge University Press, Cambridge. ISBN 0 521 770513.

Morton, O. 1992. Charophyta. pp.91 - 94 in Hackney, P. (Ed) 1992 Stewart and Corry's Flora of the North-east of Ireland. Third edition. Institute of Irish Studies. The Queen's University of Belfast.

Stewart, N.F. and Church, J.M. 1992. Red Data Book of Britain and Ireland: Stoneworts. The Joint Nature Conservation Committee, Peterborough. ISBN 1 873701 24 1.

Lloyd, James. 2007. "Cytoskeletal Structures Responsible for Cytoplasmic Streaming in Chara." St. Vincent-St. Mary High School in Accordance with Dr. Donald Ott of The University of Akron. (Science Inquiry)