Charophyta

Charophyta is a division of freshwater green algae. The terrestrial plants, the Embryophyta emerged within Charophyta, with the class Zygnematophyceae as a sister group. 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 parenchymatous charophytes that are the closest relatives of the land plants, where flagellate sperm are also present in all except the conifers and flowering plants. Fossil stoneworts 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 Chlorophyta and within which the Embryophyta emerged. 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, cellulose in the cell wall and the use of starch, stored in the plastids, as a storage polysaccharide. Unlike chlorophytes, the 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.