Vascular plant

From New World Encyclopedia
Vascular Plants
Scientific classification
Kingdom: Plantae (in part)
'Divisions'

The vascular plants are plants in the Kingdom Plantae (also called Viridiplantae) that have specialized tissues for conducting water. Vascular plants include the ferns, clubmosses, horsetails, flowering plants, conifers and other gymnosperms. Scientific names are Tracheophyta and Tracheobionta, but neither is very widely used. Nonvascular plants include both earlier-derived lineages in Plantae (mosses, hornworts, and liverworts) and members of other kingdoms (the various algae).

Vascular plants are named from the latin word vasculum, meaning "vessel" or "duct." The evolution of this vascular tissue allowed for an early dominance of these plants on land (first appearing 430 million years ago during the Silurian period), giving them the ability to transport water and dissolved minerals through specialized strands of elongated cells that run from the plant root to the tips of the leaves.

The vascular plants evolved several important features:

  1. Vascular plants have water-carrying tissues, enabling the plants to evolve to a larger size. Non-vascular plants lack these and are restricted to relatively small sizes.
  2. In vascular plants, the principal generation phase is the large, dominant, nutritionally-independent sporophyte, which is diploid with two sets of chromosomes per cell. In non-vascular plants, the principal generation phase is often the gametophyte, which is haploid with one set of chromosomes per cell.
  3. Specialized leaves, stems and roots
  4. Vascular plants have cuticles and stomata to prevent dessication and facilitate gas exchange, respectively.
  5. Evolution of seeds.

Water transport happens in either xylem or phloem: the xylem carries water and inorganic solutes upward toward the leaves from the roots, while phloem carries organic solutes throughout the plant.

Growth

Vascular plants first only developed by primary growth, in which the plants grew through cell division of the plant body. The early vascular plants did not have differentiated stems, leaves, or roots. They did, however, contain vascular cylinders, which perform the same role as the xylem and phloem in vascular plants today. Secondary growth developed early (the Devonian period, 380 million years ago) in the evolution of vascular plants, which allowed for cell division to take place in the active regions of the plant's periphery. This was an important evolutionary trait that allowed for plants to grow in diameter and form tree-like growth. During this time, vascular plants were able to expand greatly in size.

Seed Plants

Seeds developed in more advance vascular plants about 360 million years ago, and are now classified as either angiosperms or gymnosperms, and collectively called the seed plants. In these plants, the gametophytes are highly reduced. The seed contains an embryo, which is protected by a hard outer coating. The embryo's, or sporophyte's, growth has been temporarily arrested, and seeds can remain dormant until appropriate reproductive conditions prevail. Seeds allow for rooted plants to disperse and increase their range. Because of its resistence to predation, drought, and other factors, seed development was instrumental in the dominance of seed plants on land. The seed-bearing vascular plants are grouped under the superdivision Spermatophyta. The phyla include Pinophyta (conifers),Cycadophyta (cycads), Ginkgophyta (ginkgoes), Gnetophyta (gnetophytes), and Magnoliophyta (flowering plants).

These groups are discussed in more detail in the gymnosperm and angiosperm articles.

Seedless Plants

Seedless plants developed before the seed plants and include four phyla of living vascular plants, including Pteridophyta, Equisetophyta (horsetails), Lycopodiophyta (clubmosses, spikemosses, and quillworts), and Psilotophyta (whisk ferns). All of these phyla form antheridia and archegonia and produce free-swimming sperm, which require water to fertilize. Much like bryophytes, they reproduce with spres, but the sporophytes of these phyla are far more complex than those of the [[bryophyte]s, in that they have vascular tissue and well-differentiated leaves, roots, and stems.

These phyla are covered more extensively in the plant article.


References
ISBN links support NWE through referral fees

  • Mauseth, J.D. 2003. Botany: an introduction to plant biology. Jones and Bartlett Publishers. ISBN 0763721344
  • Raven, P.H. and G.B. Johnson. 1996. Biology. (Fourth Edition). Wm.C. Brown Publishers. ISBN 0697225704

See also


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