Bryophytes: The Liverworts, Hornworts, and Mosses

A long honored system of classification divides the plant kingdom into two subkingdoms: Thallophyta (which includes all plants lacking roots, stems, leaves, and vascular tissues) and Embryophyta (by definition, plants having embryos). The embryos in Embryophyta are contained within the female structure called the archegonium, which develops ont he gametophyte plant. The embryo represents the early stages of the sporophyte generation. In this group, the reproductive organs (antheridia and archegonia) are multicellular. They are oogam(Occurring as egg and sperm) and exhibit alternation of generations. Embryophyta is divided into two phyla: Bryophyta and kacheophyta. Whereas the tracheophytes are the vascular plants, the bryophytes are the liverworts, hornworts, and mosses. It is to the bryophytes that we now turn our attention.

Bryophytes include a group of very small plants having no conducting tissues. Whereas they have rhizoids (which penetrate the soil and are able to take up water), they lack vascular tissue such as xylem and phloem (which occur in higher plants). Bryophytes can also absorb water from the air. The gametophyte is the “conspicuous” generation (somewhat of a misnomer because the plant is actually quite inconspicuous and just more visible than the sporophyte). This distinction is important. (In ferns, the roles are reversed the sporophyte is considered the conspicuous generation.)