in Botany, the trivial name of the lichen, fucus, and several other plants of the cryptogamia clas.

ALGÆ, Flags; one of the seven families or natural tribes into which the whole vegetable kingdom is divided by Linnaeus, in his Philosophia Botanica. They are defined to be plants, whose root, leaf, and stem, are all one. Under this description are comprehended all the sea-weeds, and some other aquatic plants. In the sexual system, they constitute the 3d order of the 24th clas, Cryptogamia; in Tournefort, the second genus of the second section, Marine, aut Fluviatiles, of the 17th clas, Alperae vulgo habite; and the 57th order in Linnaeus's Fragments of a Natural Method. The difficulties made in this part of the vegetable kingdom are uncertain, and imperfect; and the attempts, in particular, to arrange flags by the parts of the fructification, have not been attended with great success. Dillenius has arranged this order of plants from their general habit and structure; Michelius from the parts of fructification.