Algae are usually thought of as a type of aquatic plant or slimy substance. In Latin,the name algae means "seaweed" and yet not every type of algae take the form of a weed or lives in the sea. Some varieties live in soil and can withstand long periods without water;other live in snow or inside other animal species. Although scientists agree that there are four types of algae,each distinguished by different pigmentations,the classification of all but one type remains precarious.
Blue-green algae, like all other algae,use photosynthesis, the conversion of sunlight into energy,for nourishment,and thus contain the pigment chlorophyll, an essential element in photosynthesis. what most distinguishes blue-green algae form the other three types of algae, however, is their lack of distinct nucleus. This trait has helped scientists to place them firmly in the Kingdom Monera along with bacteria.
Red brown, and green algae may be considered worlds apart from blue-green algae with respect to their classification.these algae may be single-celled like blue-green algae, or they may be as complex as some of the largest ocean-dwelling plants.None of them have leaves, flowers,roots,stems, or seeds like true plants, but many scientists assume that today's floras have evolved gradually from these algae. The debate than revolves around the classification of red, brown,and green algae with higher plants in the Kingdom Plantae, or in the mixed Kingdom Protista. The Kingdom Protista is a sort of "catchall"Kingdom,which includes both single-celled and multi-celled organisms.