%thallogen%

n. [ Gr. &unr_; 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, algae, 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. [ 1913 Webster ]