The algae are similar to the plants in that they can also photosynthesise but are usually single-celled organisms, or grow at best in small colonies, as a chain of cells (filament) or simple structures (thallus). They have life cycles as well as cell wall structures, carbohydrate reserves and pigments that are unlike those of the plants. Indeed, some have no cell walls. Only the larger species (macroalgae) will be treated here.

Brown Algae Phylum Phaeophycota Brown algae are an almost exclusively marine group. They are multicellular, often with complex anatomy and morphology. The photosynthetic pigments include chlorophylls a and c, xanthophylls and carotenes. Most occur in cooler regions. Dictyota sp. (Class Phaeophyceae, Family Dictyotaceae) are found in most of the larger and less disturbed mangrove areas locally. The thallus consists of flattened dichotomously branching structures which often overlap each other. At the mid intertidal zone, on mangrove tree roots. Rare.	Thallus of Dictyota sp. Close-up of thallus of Dictyota sp.
Green Algae Phylum Chlorophycota Green algae possess the photosynthetic pigments chlorophylls a and b, alpha-, beta- or gamma-carotenes and xanthophylls. For storage, starch is the main product. Members have very similar metabolism to the plants and are considered by most to be their ancestors. Chaetomorpha gracilis (Class Chlorophyceae, Family Cladophoraceae) France, Mediterranean, Jamaica. Locally, in most areas. Forms loose balls of filaments on mangrove roots, on mud or as a surface on mud balls, dirty dark green when wet and bright grass green when dry; the multi-nucleate cells are cylindrical, joined together as filaments which bear no rhizoids (root-hair like cells); cell walls are glass-like. No known economic value. Common. Previously known as Lola gracilis.	Numerous filaments of Chaetomorpha gracilis, resembling green glass wool Green algae forms a lawn-like surface
Red Algae Phylum Rhodophycota Red algae usually consist of filamentous forms but unlike the other algae, never possess flagella (a tiny, whip-like organelle for locomotion) at any stage of their life cycle. Their red colour is due to the pigment phycoerythrin, but they may be brown, black or purple owing to another pigment, phycocyanin. A common species, Catenella sp. (Class Rhodophyceae, Family Rhabdoniaceae), has a dark reddish branching thallus which is constricted into segments (resembling a prickly pear cactus). It grows on muddy substrates and is sometimes eaten in the Orient, e.g. C. impudica in Myanmar.	Thallus of Catenelia sp. Habitat of Catenelia sp.