Charales

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iStoneworts

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-like 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. 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 sperm. 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 vascular and non-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.

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: Stoneworts. The Joint Nature Conservation Committee, Peterborough.