The name cryptogams (scientific name Cryptogamae) is a term fairly widely in use as a phrase of convenience, although regarded as an obsolete taxonomic term. The name cryptogams refers to plants (in the wide sense of the word) which reproduce by spores. Other names, such as "thallophytes", "lower plants" and "spore plants" are also occasionally used. The best known groups of cryptogams are algae, lichens, mosses and ferns .
The name Cryptogamae is from the Greek kryptos, meaning "hidden" and gameein, "to marry". As a group Cryptogamae are the opposite of the Phanerogamae (Greek phaneros = "visible") or Spermatophyta (Greek sperma = "seed" and phytum = "plant"), the seed plants.
At one time, the cryptogams were formally recognised as a group within the plant kingdom. In his system for classification of all known plants and animals, Carolus Linnaeus (1707–1778) divided the plant kingdom into 25 classes , one of which was the Cryptogamia. This included all plants with concealed reproductive organs. He divided the Cryptogamia into four orders: Algae, Musci (bryophytes), Filices (ferns), and Fungi .
Currently, not all cryptogams are treated as part of the plant kingdom; the fungi, in particular, are regarded as a separate kingdom, more closely related to animals than plants, while some algae are now regarded as allied with the bacteria. Therefore, in contemporary plant systematics "Cryptogamae" is not a name of a scientifically coherent group, but is cladistically polyphyletic. However, all organisms known as cryptogams belong to the field traditionally studied by botanists and the names of all cryptogams are regulated by the International Code of Botanical Nomenclature.