Real Dictionary

algae
Algae is a type of plant with no stems or leaves that grows in water or on damp surfaces.

algae in American English
any of several divisions of simple photosynthetic organisms, esp. certain thallophytes, variously one-celled, colonial, or filamentous, containing chlorophyll and other pigments (esp. red and brown), and having no true root, stem, or leaf: algae are found
plural noun: any of numerous groups of chlorophyll-containing, mainly aquatic eukaryotic organisms ranging from microscopic single-celled forms to multicellular forms 100 ft. (30 m) or more long, distinguished from plants by the absence of true roots, stems, and leave

algae in British English
plural noun: unicellular or multicellular organisms formerly classified as plants, occurring in fresh or salt water or moist ground, that have chlorophyll and other pigments but lack true stems, roots, and leaves. Algae, which are now regarded as protoctists, include