"In systems in which the algae and fungi are regarded as plants, they are often grouped as a subkingdom Thallophyta, the thallophytes: organisms with no highly differentiated tissues, such as root, stem, or leaf, and no vascular tissues (xylem and phloem). The land plants are then grouped into a second subkingdom, Embryophyta, in which the zygote develops into a multicellular embryo still encased in an archegonium or an embryo sac. All embryophytes are marked by alternation of generation.
Although they are no longer used in schemes of classification, terms such as "algae," "thallophytes," and "gymnosperms" are still sometimes useful in an informal sense. An even earlier scheme divided all plants into "phanerogams," those with flowers, and "cryptogams," those lacking flowers; these terms are occasionally seen today also."

Biology of Plants, Fourth Edition, Worth Publishers Inc., Stanford University, Peter H. Raven and Helena Curtis, ©1971

In the first aquatic plants, tissues for support and conduction (vascular) were not necessary. On land, fundamental adaptations were necessary to transport nutrients throughtout the organism's body. With the development of pollen and seeds in gymnosperms the dependence of plants on water for fertilization was eliminated enabling new species to thrive and become more widely distributed on land.

In light of their evolution the relationships among the different groups of non-flowering plants is not fully known. The illustration represents several points of view fused into a singular one. Mosses, Liverworts and Hornworts are placed with Embryophytes. Ferns, Gymnosperms, Club Mosses and Horsetails are grouped as Vascular Plants.

The plant body of a Thallophyte is a thallus, which may consist of a single cell or large mass of undifferentiated cells that show negligible specializations except those related to reproduction. Thallophytes lack conductive (vascular) tissue. They possess no roots, stems, leaves and do not produce flowers, seeds or fruits.

Typically they have single cell reproductive structures. Those that are multi-cellular lack a jacket of sterile cells around sex cells and around the spores. Stoneworts were an exception. The fertilized egg or zygote of Thallophytes do do not develop into an embryo. Also, reproduction occurs asexually by cell division or through formation of spores of many types, motile and non-motile.


References and Further Reading

  • A Golden Guide - Non-Flowering Plants ©1967
  • Biology of Plants, Fourth Edition, Worth Publishers Inc., Stanford University, Peter H. Raven and Helena Curtis, ©1971
  • Zoology Quest: Embryophyte
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