Green algae

The green algae or Chlorophyta sensu lato is the paraphyletic group of algae closely related to land plants. Some sources still use the term Chlorophyta and earlier Chlorophyceae, but later these terms have been used to delimit subgroups, such that the group "green algae" as a taxon it has become informal, considering that taxonomically it includes the groups of algae Chlorophyta and Charophyta.

Some 10,000 different species have so far been described as green algae, being the most diverse of all algae. Although they are also found in the seas, they are most diverse in inland waters (freshwater) encompassing a wide variety of habitats. Many are unicellular, frequently flagellated, but others develop multicellular forms that are never very complex.

There is presence of pigments such as chlorophyll a and b, β-carotene and xanthophylls, as well as reserve substances (starch), as is also found in terrestrial plants (kingdom Plantae stricto sensu), which which reveals his kinship with them. Today it is accepted that land plants are derived from freshwater green algae of the division Charophyta.

General information

They are found in very diverse habitats, even in very adverse conditions. Only 10% of the species are marine, the rest are freshwater. There are forms, such as Pleurococcus, capable of developing in the air in very humid environments. The gonidia, algae, of lichens are most often green algae. In the sea they are distributed wherever there is sufficient sunlight to carry out photosynthesis.

Green algae can be unicellular, often flagellate, or multicellular with stems that are never very complex. Most of the species are benthic (linked to the bottom) but there are planktonic ones, which live in suspension and are one of the main components of phytoplankton. They present flagellated cells (isoconts), photosynthetic and contain chlorophyll a and b; chloroplasts contain starch; and the thylakoids are anastomosed.

They can reproduce asexually, by mobile spores, or sexually, by fertilizing an oosphere (female gamete) by a frequently flagellated male gamete (anterozoid). They have simple reproductive structures, the most complex (Chara) present the oogonia wrapped. Spores and gametes are formed from the entire contents of a mother cell. Great diversity of shapes and sizes. Some resemble higher plants in that they have "organs" similar to stems, leaves and roots. Some live in association with fungi forming lichens.

Name

Green alga refers by translation to the scientific name Chlorophyta —castilianized as chlorophytas or chlorophytes—. All these names, except for clarification of their constituency, are of generally indistinct use in non-specialized literature. However, taxonomically the group includes both Chlorophyta (chlorophyte green algae) and Charophyta (non-chlorophyte green algae), which is the part of the Streptophyta clade that does not include Embryophyta (land plants).

Phylogeny

Conceptually the "green algae" they can be systematically considered as a paraphyletic group, although the group that includes green algae and land plants is monophyletic and constitutes the clade Viridiplantae (sometimes restrictedly considered as kingdom Plantae).

Updated phylogenetic tree of the different groups of viridofites.

Taxonomically, green algae are usually classified into two divisions (or phyla):

• Chlorophyta is a nail that depends on the classification criteria, is framed or in the Protist kingdom or in the Plantae kingdom.

• Charophyta is a paraphytic group within the Streptophyta nail.