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.