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One of the two commonly recognized subkingdoms of plants, encompassing the euglenoids and various classes of algae. In contrast to the more closely knit subkingdom Embryobionta, the Thallobionta (often also called Thallophyta) are diverse in pigmentation, food reserves, cell-wall structure, and flagellar structure. The Thallobionta are united more by the absence of certain specialized tissues or organs than by positive resemblances. They do not have the multicellular sex organs commonly found in most divisions of Embryobionta. Many of the Thallobionta are unicellular, and those which are multicellular seldom have much differentiation of tissues. None of them has tissues comparable to the xylem found in most divisions of the Embryobionta, and only some of the brown algae have tissues comparable to the phloem found in most divisions of the Embryobionta.
A large proportion of the Thallobionta are aquatic, and those which grow on dry land seldom reach appreciable size. The Thallobionta thus consist of all those plants which have not developed the special features that mark the progressive adaptation of the Embryobionta to life on dry land. See Plant kingdom