Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largelyaquatic (both fresh water and marine) organisms. They occur in avariety of other habitats: moist stones, soils and wood. Some of them also occur in association with fungi (lichen) and animals (e.g., on sloth bear).

Feature	Description
General Characteristics of Algae
Common Name	Algae
Habitat	Aquatic (freshwater and marine), moist stones, soils, wood, in association with fungi (lichen), on animals (e.g., sloth bear)
Plant Kingdom	Chlorophyll-bearing, simple, thalloid, autotrophic organisms
Form and Size	Highly variable, from colonial forms (Volvox) to filamentous forms (Ulothrix, Spirogyra), massive plant bodies (kelps)
Vegetative Reproduction	By fragmentation, each fragment develops into a thallus
Asexual Reproduction	By production of spores, most common being zoospores (flagellated, motile), germinate to form new plants
Sexual Reproduction	By fusion of gametes, can be isogamous, anisogamous, or oogamous
Isogamous Reproduction	Fusion of similar gametes, flagellated (e.g., Ulothrix) or non-flagellated (e.g., Spirogyra)
Anisogamous Reproduction	Fusion of dissimilar gametes, e.g., Eudorina
Oogamous Reproduction	Fusion of one large non-motile female gamete and a smaller motile male gamete, e.g., Volvox, Fucus
Economic Importance	Significant for CO₂ fixation, primary producers of energy-rich compounds, food sources (e.g., Porphyra, Laminaria, Sargassum), hydrocolloids (e.g., algin, carrageen), agar production, protein-rich food supplements (e.g., Chlorella)
Ecological Importance	Increase dissolved oxygen through photosynthesis, basis of aquatic food cycles
Divisions	Chlorophyceae, Phaeophyceae, Rhodophyceae
Chlorophyceae (Green Algae)
Common Name	Green algae
Plant Body	Unicellular, colonial, or filamentous; grass green due to chlorophyll a and b
Chloroplasts	Discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon-shaped
Storage Bodies	Pyrenoids (protein and starch)
Cell Wall	Rigid, inner layer of cellulose, outer layer of pectose
Reproduction	Vegetative (fragmentation), asexual (flagellated zoospores), sexual (isogamous, anisogamous, oogamous)
Examples	Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara
Major Pigments	Chlorophyll a, b
Stored Food	Starch
Flagellar Number and Position	2-8, equal, apical
Habitat	Freshwater, brackish water, salt water
Phaeophyceae (Brown Algae)
Common Name	Brown algae
Habitat	Primarily marine
Plant Body	Simple branched forms (Ectocarpus) to profusely branched kelps (up to 100 meters); usually attached to substratum by a holdfast, with a stalk (stipe) and leaf-like photosynthetic organ (frond)
Pigments	Chlorophyll a, c, carotenoids, xanthophylls (fucoxanthin)
Colour	Olive green to brown
Storage Food	Laminarin, mannitol
Cell Wall	Cellulosic, covered with gelatinous coating of algin
Vegetative Reproduction	By fragmentation
Asexual Reproduction	By biflagellate zoospores, pear-shaped with two unequal laterally attached flagella
Sexual Reproduction	May be isogamous, anisogamous, or oogamous; union of gametes can occur in water or within the oogonium (oogamous species); gametes are pyriform with two laterally attached flagella
Examples	Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus
Major Pigments	Chlorophyll a, c, fucoxanthin
Stored Food	Mannitol, laminarin
Flagellar Number and Position	2, unequal, lateral
Habitat	Freshwater, brackish water, salt water
Rhodophyceae (Red Algae)
Common Name	Red algae
Habitat	Marine, found in warmer areas, at various depths
Plant Body	Multicellular, some with complex body organisation
Pigments	Chlorophyll a, d, phycoerythrin
Stored Food	Floridean starch (similar to amylopectin and glycogen)
Cell Wall	Cellulose, pectin, and poly sulfate esters
Reproduction	Vegetative (fragmentation), asexual (non-motile spores), sexual (oogamous with complex post-fertilization developments)
Examples	Polysiphonia, Porphyra, Gracilaria, Gelidium
Major Pigments	Chlorophyll a, d, phycoerythrin
Stored Food	Floridean starch
Flagellar Number and Position	Absent
Habitat	Freshwater (some), brackish water, salt water (most)