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Charophyta
Scientific classification
Domain:	Eukaryota
(unranked):	Archaeplastida
Kingdom:	Viridiplantae
(unranked):	Streptophyta
Division:	Charophyta
Groups included
Mesostigmatophyceae Klebsormidiophyceae Zygnematophyceae Zygnematales Desmidiales Charophyceae Coleochaetales Charales

The Charophyta are a division of freshwater green algae that includes the class Charophyceae, a sister group to the terrestrial plants, the Embryophyta. In some charophyte groups, such as Zygnematophyceae or conjugating green algae, flagellae are absent and sexual reproduction does not involve free-swimming flagellate sperm. Flagellate sperm, however, are found in stoneworts (Charales) and Coleochaetales, orders of parenchymous charophytes that are the closest relatives of the land plants, where flagellate sperm are also present in all except the conifers and flowering plants. Fossils of a stonewort of Devonian age that are similar to those of the present day have been described from the Rhynie chert of Scotland.

Classification

Charophyta are complex green algae that form a sister group to the Chlorophyceae and the Embryophyceae. The chlorophyte and charophyte green algae and the embryophytes or land plants form a clade called the green plants or Viridiplantae, that is united among other things by the absence of phycobilins, the presence of chlorophyll b and chlorophyll a and the use of starch as a storage polysaccharide. Charophytes and embryophytes share the same mechanism of cell division using a phragmoplast as a framework for assembly of the new dividing cell wall. Thus Charophyta and Embryophyta together form the clade Streptophyta, excluding the Chlorophyta. Because the Charophyta do not include all descendents of their common ancestor with the embryophytes they form a paraphyletic group.

Description

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The charophytes are obligate water plants, growing submerged in calcareous fresh water. They are distributed throughout the world from the tropics to cold temperate zones. Charophytes such as Palaeonitella cranii and possibly the yet unassigned Parka decipiens are present in the fossil record of the Devonian. Palaeonitella differed little from some present-day stoneworts.

The various groups included in the Charophyta have diverse and idiosyncratic reproductive systems, sometimes with complex reproductive organs. The unique habit among the algae of protecting the overwintering zygote within the tissues of the parent gametophyte is one of several characteristics Coleochaetales that suggest that they are a sister group to the embryophytes.

The Charales or stoneworts are freshwater plants with slender green or grey stems; the grey colour of many species results from the deposition of lime on the walls, masking the green colour of the chlorophyll. The main stems are slender and branch occasionally. Lateral branchlets occur in whorls at regular intervals up the stem. The reproductive organs consist of antheridia and oogonia, though the structures of these organs differ considerably from the corresponding organs in other algae. As a result of fertilization a protonema is formed, from which the sexually reproducing plant develops.

Charophytes are frequently found in hard water with dissolved calcium or magnesium carbonates. They tolerate low concentrations of salt, and are found in the inner reaches of the Baltic Sea and in tropical brackish lagoons but not in marine environments. The water must be still, or only slow­-flowing, oligotrophic or mesotrophic and little pollution due to sewage.

Cell structure

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There are numerous small discoid chloroplasts, which are disposed around the periphery of the cells. No pyrenoids are present. The large internodal cells are sometimes multinucleate, and their nuclei often possess large nucleoli and scanty chromatin. In these cells the cytoplasm forms only a peripheral layer with a large central vacuole. The cell walls are composed of cellulose, though there may be also a superficial layer of a more gelatinous material of unknown composition.

The storage material is starch, except in the oospore, where oil also occurs. This starch also accumulates in special storage structures, termed bulbils, which consist of rounded cells of varying size which are developed in clusters on the lower stem and root nodes. They are mainly developed when plants are growing in fine slimy mud.

Cytoplasmic streaming was first demonstrated in the giant cells of Chara internodes by Giovanni Battista Amici, in 1818.

Sexual reproduction

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The reproductive organs of the Charales show a high degree of specialization. The female organ is a large oval structure with an envelope of spirally arranged, bright green filaments of cells. It is termed an oogonium. The male organ is also large, bright yellow or red in colour, spherical in shape, and is usually termed an antheridium, though some workers regard it as a multiple structure rather than a single organ. The sex organs are developed in pairs from the adaxial nodal cell at the upper nodes of the primary lateral branches, the oogonium being formed above the antheridium. They are sufficiently large to be easily seen with the naked eye, especially the bright orange or red antheridium. Many species are dioecious. In others the monoecious condition is complicated by the development of the antheridium before the formation of the oogonium, thus preventing fertilization by antherozoids of the same plant. In this case the two types of sex organs usually arise from different points on the lateral branches

Vegetative propagation

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Vegetative propagation occurs readily in the Charales. Secondary protonemata may develop even more rapidly than primary ones. Fragments of nodes, dormant cells of plants after hibernation or the basal nodes of primary rhizoids may all produce these secondary protonemata, from which fresh sexual plants can arise. It is probably this power of yegetative propagation which explains the fact that species of Characeae are generally found forming dense clonal mats in the beds of ponds or streams, covering quite large areas.

References

1. Lewis, Louise A.; Richard M. McCourt (2004). "Green algae and the origin of land plants" (abstract). American Journal of Botany. 91 (10): 1535–1556. doi:10.3732/ajb.91.10.1535. PMID 21652308.
2. Karol KG, McCourt RM, Cimino MT, Delwiche CF (December 2001). "The closest living relatives of land plants". Science. 294 (5550): 2351–3. Bibcode:2001Sci...294.2351K. doi:10.1126/science.1065156. PMID 11743201.{{cite journal}}: CS1 maint: multiple names: authors list (link)
3. Vaughn, K.C.; Renzaglia, K.S. (2006). "Structural and immunocytochemical characterization of the Ginkgo biloba L. sperm motility apparatus". Protoplasma. 227 (2–4): 165–73.
4. ^ Kelman, R.; Feist, M.; Trewin, N.H.; Hass, H. (2003). "Charophyte algae from the Rhynie chert". Transactions of the Royal Society of Edinburgh: Earth Sciences. 94 (4): 445–455.
5. Tree of Life: Green plants
6. Hemsley, A.R. (1989). "The ultrastructure of the spores of the Devonian plant Parka decipiens". Annals of Botany. 64 (3): 359–367.
7. Becker, B.; Marin, B. (2009). "Streptophyte algae and the origin of embryophytes". Annals of Botany. 103 (7): 999–1004. doi:10.1093/aob/mcp044. PMC 2707909. PMID 19273476.
8. Schubert, H.; Blindow, I. (2004). Charophytes of the Baltic Sea. Gantner Verlag. ISBN 3906166066.
9. Palma-Silva, C.; Albertoni, E.F.; Esteves, F.A. (2004). "Charophytes as nutrient and energy reservoir in a tropical coastal lagoon impacted by humans (RJ, Brazil)". Brazilian Journal of Biology. 64: 479–487.

v t e Early land flora
Related links	Evolutionary history of plants Rhynie chert
The first...?	Vascular plant, Cooksonia Tree, Wattieza Lycophytes, the Drepanophycales and the zosterophylls Fungus fossil, Ornatifilum Lichen, Spongiophyton
Enigmatic taxa	Cuticular remains: Bitelaria Cosmochlaina Nematothallus Orestovia Protosalvinia Spongiophyton Other: Pachytheca Prototaxites.
Sister taxa	Green algae: Charophyta, from which land plants evolved Chaetocladus, an early alga

• Charophyta
• Green algae
• Plants
• Plant divisions