One of the two plant subkingdoms, the other being the Thallobionta. The Embryobionta are here considered to include eight divisions, the Rhyniophyta, Bryophyta, Psilotophyta, Lycopodiophyta, Equisetophyta, Polypodiophyta, Pinophyta, and Magnoliophyta. The Rhyniophyta are represented only by Paleozoic fossils, but the other seven divisions have both modern and fossil representatives. See the separate articles on each division.
The Embryobionta differ from the green algae (Chlorophyta) and from most Thallobionta in that the normal life cycle of the Embryobionta shows a well-marked alternation of generations in which the sporophyte (spore-producing, typically diploid) generation always begins its development as a parasite on the gametophyte (gamete-producing, typically haploid) generation. The young sporophyte is called an embryo.
The more primitive divisions of Embryobionta have the gametes produced in multicellular sex organs (archegonia and antheridia), in contrast to the unicellular oogonia and antheridia of the Thallobionta in general. In the more advanced divisions (Pinophyta and Magnoliophyta) of Embryobionta, the antheridia and archegonia are highly modified or entirely suppressed, in conformity with the general reduction of the gametophyte generation.
All divisions of Embryobionta except the Bryophyta have specialized conducting tissues (xylem and phloem) in the sporophyte. With the exception of most bryophytes, they also commonly have a characteristic stomatal apparatus which controls the opening and closing of numerous tiny pores (stomates) in the leaves and stems in response to environmental conditions. These specializations, together with the progressive reduction of the gametophyte in the more advanced divisions, reflect the progressive evolutionary adaptation of the Embryobionta to life on dry land instead of in the ancestral water. The Embryobionta are therefore often called the land plants, in spite of the fact that many of them, such as the water lilies, have returned to an aquatic habitat. The seven divisions of Embryobionta which characteristically have xylem and phloem have sometimes been treated as a single comprehensive division under the name Tracheophyta. See Plant kingdom, Thallobionta