Author: Jan Scholten
Archaeplastidae is a very big group from early evolution. It can be expressed as plants, broadly defined. A big part of it are the red and brown algae, which were formerly considered to belong to the Algae of the Plant kingdom. Recently they have been split off and treated as a separate group including other one-cellular organisms. They lack chlorophyll, which the green algae and more generally the Viridaeplantae have.
In the Plant theory the first 2 groups, Rhodophyta and Glaucophyta, are treated as the first group of the Plant kingdom, connected with the Hydrogen series. As such this group is polypheletic because Chlorophyta are not included. As discussed elsewhere this is done as the group has very distinctive qualities. Evolution has led to new groups but they have very distinct qualities such as containing chlorophyll.
In the Apg3 classification Archaeplastidae consists of:
1. Rhodophyta: Coloured groups (algae-like).
2. Glaucophyta: Colourless groups (fungus-like).
3. Chloroplastida, Viridiplantae: green algae and land plants.
In the Plant theory Archaeplastidae consists only of Rhodophyta and Rhodophyta. Viridiplantae is treted as a separate Phylum; thye have chlorophyll.
Algae is an informal term for a large and diverse group of plants. They are often not closely related and are thus polyphyletic. A definition algae could be plants that have chlorophyll and lack a sterile covering of cells around their reproductive cells.
Most algae are aquatic and autotrophic; they lack leaves, roots, stem, vessels, flowers, stomata, xylem, phloem.
Foms of algae:
Unicellular genera, such as Chlorella and the diatoms
Brown algae, mulitcellualr, like kelp.
Charophyta, freshwater algea, in green algae.
Cyanobacteria: blue-green algae, sometimes not considered to be algae.
Green algae or Viridiplantae: have chloroplasts derived from endosymbiotic cyanobacteria.
Diatoms: algae with secondary chloroplasts derived from an endosymbiotic red alga.
Cryptogamae or Cryptogam are plants that reproduce by spores, without flowers or seeds. Cryptogamae means hidden (kryptos) reproduction (gamein, marry). The opposite is Spermatophyta, plants produicing seeds.