Thallogen
Thal"lo*gen\, n. [Gr. ? young shoot or branch, frond + -gen.] (Bot.) One of a large class or division of the vegetable kingdom, which includes those flowerless plants, such as fungi, alg[ae], and lichens, that consist of a thallus only, composed of cellular tissue, or of a congeries of cells, or even of separate cells, and never show a distinction into root, stem, and leaf.