The thallophytes (Thallophyta or Thallobionta) are a polyphyletic group of non-mobile organisms traditionally described as "thalloid plants", "relatively simple plants" or "lower plants". They were a defunct division of kingdom Plantae that included fungus, lichens and algae and occasionally bryophytes, bacteria and the Myxomycota. Thallophytes have a hidden reproductive system and hence they are also called Cryptogamae (together with ferns), as opposed to Phanerogamae. The thallophytes are defined as having undifferentiated bodies (thalli), as opposed to cormophytes (Cormophyta) with roots and stems.
Several different definitions of the group have been used.
Stephan Endlicher, a 19th-century Austrian botanist, separated the vegetable kingdom into the thallophytes (algae, lichens, fungi) and the cormophytes (including bryophytes and thus being equivalent to Embryophyta in this case) in 1836. This definition of Thallophyta is approximately equivalent to Protophyta, which has always been a loosely defined group.
In the Lindley system (1830–1839), Endlicher's cormophytes were divided into the thallogens (including the bryophytes), and cormogens ("non-flowering" plants with roots), as well as the six other classes. Cormogens were a much smaller group than Endlicher's cormophytes, including just the ferns (and Equisetopsida) and the plants now known as lycopodiophytes.