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THALLOGEN
One of a bigclass 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 distinctioninto root, stem, and leaf.
Origin: Gr. Young shoot or branch, frond + -gen.
Source: Websters Vocabulary