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Life / Eukarya / Plantae / Viridiplantae / Charophyta / Charophyceae / Charales
1. Nitellaceae
2. Characeae

The charophycean algae are generally known as stoneworts. Stoneworts are macroscopic (growing up to 120cm long) green algae inhabiting in freshwater. Many species are endangered by water pollution and eutrophication. The fossil records date back to the Silurian period (ca. 420 mya).

The charophycean thallus is differenciated into a main axis, whorl branches ("leaves") and rhizoids. The main axis and lateral branches are composed of nodes and internodes. The node is sometimes covered by cortex derived from node cell. The internode cell is very large (sometimes reaches a few centimeters in length), thus it is a good material to observe cytoplasmic streaming. Main compornent of cell wall is cellulose synthesized from rosette terminal complexes in plasma membrane. The thalli are sometimes encrusted in calcium carbonate (thus called stoneworts). The cell possesses many discoid chloroplasts without pyrenoid. Young cells are uninucleate, but older cells become multinucleate. The patterns of mitosis and cytokinesis are basically same to those of land plants (i.e. open mitosis, persistent telophase spindle, cell plate with phragmoplast). Sexual reproduction is oogamous. Thalli are monoecious or dioeciaous. The ovoid oogonia and spherical antheridia are borne at nodes of lateral banches. THe oogonium is composed of a large egg cell surrounded spirally by five or ten tube cells, each of which ends in a coronula cell. The anteridium is enclosed by eight shield cells. The tuft of antheridial filaments (spermatogenous threads) are produced from the capitulum cell at the top of the manubrium cell extended inward from each shield cell. The sperm has elongated spiral shape and possesses two parallel flagella inserted subapically. The sperm is covered by small organic scales. The zygotes become oospores that germinate via meiosis after dormancy.

The term "Charophyceae" is generally used in a much broader sunse, for the green algae closely related to land plants (i.e. green algae except for the Chlorophyta sensu stricto). However, the Charophyceae of this meaning is paraphyletic.

1: Chara. 2: Lychnothamnus. 3: Nitella.