Algae dichotomous key

Blue-green Algae - Cyanobacteria

Thallus Unicellular………………………………………………………………………………………Gleocapsa sp.
Thallus Filamentous
Homocystous
3. Trichome solitary or matted together……………………….…………………….Oscillatoria sp.
3. Trichome single, spirally twisted cell……………………..……………………………Spirulina sp.
2. Heterocystous
4. Both Heterocysts and Akinetes present
5. Globular, bead-like cells, tangled trichome……………………..................Nostoc sp.
5. Spherical, barrel to sub-cylindric shaped cell, straight trichome…………………………………………………………………………………………Anabaena sp.
4. Heterocyst present, Akinetes absent………………………………………………...Rivularia sp.

Diversity of Plant-like Unicellular Eukaryotic Algae
Phylum Euglenophyta
1. Cellular organization eukaryotic; thalli solitary; pigments chlorophyll a, b, β-carotene, xanthophyll; reserved food starch………………………………………………………………………………Euglena sp.

Phylum Heterokontophyta – Class Xanthophyceae
1. Cellular organization eukaryotic; thalli siphonous; pigments carotenes, xanthophylls; reserved food leucosin, chrysolaminarin………………………………………………………………………………..Vaucheria sp.

Division Dinophyta – Class Dinophyceae
1. Marine habitat; 1 horizontal flagellum, 1 vertical flagellum; toxic………Pyrodinium bahamense
1. Marine and freshwater habitat; 2 flagella; Non-toxic; Presence of arms/horns……..Ceratium sp.

Phylum Heterokontophyta – Class Coscinodiscophyceae and Bacillariophyceae
1. Habit marine; absence of median raphe; non-motile…………………………………………………Centrales
1. Habit freshwater; median raphe present; motile……………………………………………………….Pennales

Brown Algae – Class Phaeophyceae

1. Absence of gametophyte stage…………........................................................... Fucus sp.

1. Presence of gametophyte stage
2. Calcareous……………………………………………………………………………………. Padina sp.
2. Non-calcareous
3. Single lamina blade……………………………………………………………….…Laminaria sp.
3. Many separate blades
4. Uniform membrane………………………………………………………… Colpomenia sp.
4. Non uniform membrane
5. Membrane with holes…………………………………Hydroclathrus clathratus
5. Membrane without holes
6. Stipe grows throughout the algal body……………………..Sargassum sp.
6. Stipe grows at the base of the algal body
7. Unbranched………………………………….…………………… Ectocarpus sp.
7. Branched
8. Flat branching …………………………………………………..Dictyota sp.
8. Branching is not flat
9. Flat blades……………………………………………..Hormophysa sp.
9. Blades are not flat……………………………………..Turbinaria sp.


Red Algae – Division Rhodophyta

1. Habit intertidal zones, cold water …………………………………………………………………………Porphyra sp.
1. Habit sublittoral zones, warm water
2. Thalli uniaxial………………………………………………………………………………………Polysiphonia sp.
2. Thalli multiaxial
3. Dichotomously branching, mucilaginous……………………………………………..Liagora sp.
3. Dichotomously branching, globrous
4. Tetrasporophytes isomorphic…………………………………………………Actinotrichia sp.
4. Tetrasporophytes dimorphic………………………………………………………Galaxaura sp.

Green Algae – Division Chlorophyta

Microscopic
Unicellular
Presence of mucilage………………………………………………………………………….Desmids
Absence of mucilage
Cup-shaped chloroplast………………………………………………………………..Chlorella
4. Lobe-shaped chloroplast………………………………………………………...Protococcus
2. Multicellular
5. Colonial
6. Coenobic
7. Below 50 cell count
8. 16 cell count…………………………………………………………………Pediastrum
8. 4 cell count……………………………………………………………….Scenedesmus
7. Above 50 cell count…………………………………………………………………..Volvox
6. Non-coenobic………………………………………………………………………..Hydrodictyon
5. Filamentous
9. Freshwater only…………………………………………………………………………….Ulothrix
9. Freshwater and marine
10. Branched…………………………………………………………………………Cladophora
10. Unbranched
11. Helical/Spiral………………………………………………………………..Spirogyra
11. Non-helical/spiral……………………………………………………Oedogonium
1. Macroscopic
12. Calcareous
13. Fan-shaped frond
14. Overlapping frond……………………………………………………………………………...Udotea
14. Progressing frond……………………………………………………………………………Halimeda
13. Non-fan shaped frond
15. stipe longer than frond………………………………………………………………Acetabularia
15. stipe shorter than frond………………………………………………………………..Halicoryne

12. Non-calcareous
16. Membranous
17. Intestine-like………………………………………………………….Ulva intestinales
17. Lettuce-like…………………………………………………………………..Ulva lactuca
16. Coenocytic
18. Distinguishable frond
19. Fan-like……………………………………………………………..Avrainvillea
19. Non-fan like
20. grape-like………………………………………………………….Caulerpa
20. branch-like… ……………………………………………………..Codium
18. Non-distinguishable frond
21. Detached………………………………………………………………….Valonia
22. Attached……………………………………………………………Boergesenia