Difference Between Red Algae and Green Algae

Algae are defined as chlorophyllous, thalloid, a vascular plants with no cellular differentiation. Algae are usually aquatic, either marine or fresh water. Only few algae occur in moist terrestrial habitats like tree trunks, wet rocks, moist soil etc.
Algae are usually differentiated on the basis of pigments, flagellation and storage products. 

Algae includes under Kingdom Planate by Whittaker(1969) are of red algae, brown algae and green algae.

Green Algae: Plants fresh water or marine. May be of various forms like unicellular motile(Chalmydomonas), non motile(Chlorella), clonial (Volvox, Hydrodictyon), parenchymatous (Ulva), Coenocytic (Volvox).

Red Algae: These are most showy of sea weeds and are predominantly marine. Colour is due to presence of red pigment(r-phycoerythrin) and a blue pigment(r-phycocyanin) in he chromatophores.
Example: Polysiphonia, Gelidium, Rhodymenia, Batrachospermum.

Red Algae vs Green Algae

Red Algae	Green Algae
Mostly marine	Mostly fresh water and subaerial.
Unicellular species fewer.	Unicellular species abundant.
Thylakoids are unstacked.	Thylakoids are stacked in groups of 2-20.
Chlorophyll a and d type.	Chlorophyll a and b type.
Fucoxanthin may be present.	Fucoxanthin is absent.
Phycobilins present.	Phycobilins absent.
Reserve food is floridean starch.	Reserve food is starch.
Motile stages are absent.	Present; flagella 2 to 8 apical and equal.
Cell wall contains cellulose and sulphated phycocolloids.	Cell wall is of cellulose.