CLASSIFICATION :
Artificial System of Classification :
- Used superficial morphological characters.
- Based on a few characteristics like habit, colors, number and shape of leaf.
- Mainly based on vegetative characters.
- Such system developed by Linnaeus.
Natural System of Classification :
- Based on natural affinities among organisms
- Included external as well as internal features like anatomy, embryology and phytochemistry.
- Developed by George Bentham and J. D. Hooker
Phylogenetic System of Classification :
- Based on evolutionary relationships between the various organisms.
- Organism belongs to same taxa have a common ancestors.
- Developed by Hutchinson.
Numerical Taxonomy :
- Carried out using computers
- Based on all observable characteristics
- Data processed after assigning number and codes to all the characters.
Cytotaxonomy :
- Based on cytological information.
- Gives importance to chromosome number, structure and behaviour.
Chemotaxonomy :
- Based on chemical constituents of the plants.
ALGAE :
- Chlorophyll bearing, simple, thalloid, autotrophic and mostly aquatic organisms. Moist stone, soils and wood are the other habitat.
- The size ranges from microscopic unicellular forms like Chlamydomonas, to colonial forms like Volvox and to filamentous forms like Ulothrix and Spirogyra. A few marine forms such as kelps, form massive plant bodies.
- Reproduce vegetatively by fragmentation.
- Reproduce asexually mostly by producing motile spore called zoospores.
- Reproduce sexually by producing gametes.
- Isogamous: both gametes are same size and motile
- Anisogamous: both gametes are dissimilar in size but motile.
- Oogamous: male gamete is smaller but motile, female gamete is large and non- motile.
Importance of Algae :
- At least half of the total carbon dioxide fixation on earth carried out by them.
- Increase oxygen level in the environment.
- Many species like Laminaria, Sargassum etc. are used as food.
- Agar obtained from Gelidium and Gracilaria is used in ice-creams and jellies and also used to culture bacteria.
- Algin obtained from brown algae and carrageen from red algae used commercially.
- Chlorella and Spirullina are unicellular algae, rich in protein and used as food supplement even by space travelers.
