Algae: Modern Trends in the Classification of Algae!
The classification of algae has continually been modified since its beginning in the 1753 edition of Linnaeus Species Plantarum.
In natural or phylogenetic systems (which represent real evolutionary relationships) of classification, alterations in the classification of algae are made as a result of augmentation of our knowledge.
This has resulted in the present, largely polyphyletic system (the system having many distinct lines of evolutionary history) in which the algae are grouped in seven to eleven categories of divisional rank. The criteria on which the classification is based are pigments, reserve food and flagellation.
However, our knowledge of the comparative chemistry of the several pigments and storage products is fragmentary, especially in relation to the genetics and evolution of the organisms, that it is quite possible our current polyphyletic groupings may be modified into a more monophyletic system in the future.
At the levels of orders, families and genera it has been noted that (1) In the Chlorophycophyta and Phaeophycophyta; the orders are delimited largely on vegetative or somatic characters, variation in reproduction being treated as of secondary importance. In the division Rhodophycophyta, in contrast, the orders are at present delimited on the basis of the organization of the female reproductive branch, vegetative attributes being secondary. (2) Among the Chryso- phycophyta, the families of certain orders are at present delimited on the basis of flagellar numbers while the same criterion is used at the generic level in the unicellular motile Chlorophycophyta. These examples indicate that modern classifications are, at least approximations of relationship.
Like all plants, the algae are classified in accordance with the recommendations and prescriptions of the International Code of Botanical Nomenclature. This code recognizes the individual organism as belonging to a species, the species to a genus, the genus to a family, the family to an order, the order to a class and the class to a division.
The following suffixes for use in the classification of algae have been recommended by the International Code of Botanical Nomenclature;
Sub-class-phycideae Genus-a Greek name
Order-ales Species-a Latin name
The algae have been divided into 11 divisions. They are as follows:
1. Cyanophycophyta (Blue-green algae)
2. Chlorophycophyta (Green algae)
3. Charophyta (Stoneworts)
4. Euglenophycophyta (Euglenoids)
5. Xanthophycophyta (Yellow-green algae)
6. Chrysophycophyta (Golden algae)
7. Bacillariophycophyta (Diatoms)
8. Phaeophycophyta (Brown algae)
11. Rhodophycophyta (Red algae)
Representatives belonging to few important divisions— Chlorophycophyta, Xantho- phycophyta, Phaeophycophyta and Rhodophycophyta have been discussed in detail in the present text.