The diagonistic characters of Algae are :
(a) Algae are usually aquatic, either marine or fresh water.
(b) Plant body is unicellular, colonial, filamentous, parenchymatous or pseudoparenchymatous.
(c) Algae, like other aquatic plants, are covered over by mucilage. Mucilage protects the algae from epiphytic growth and decaying effect of water.
(d) Vascular tissues are absent.
(e) A mechanical tissue is absent. The algae are held upright in water due to buoyancy provided by the latter.
(f) Nutrition is photosynthetic.
(g) Plants contain chlorophyll a, carotenes and xanthophylls. Additional pigments occur in specific groups.
(h) Vegetative and asexual modes of reproduction are abundant. Asexual spores are of two types, mitospores and meiospores.
(i) Sexual reproduction involves isogamy, anisogamy and oogamy in different groups.
(j) An embryo stage is absent.