Seedless Vascular Plants

3 Key excerpts on "Seedless Vascular Plants"

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  Scientific American Science Desk Reference

  • (Author)
  • 2008(Publication Date)
  • Trade Paper Press

    (Publisher)

  angiosperms (flowering plants) are all vascular plants.

  vegetative reproduction type of asexual reproduction in plants that relies not on spores, but on multicellular structures formed by the parent plant. Some of the main types are stolons and runners, sucker shoots produced from roots (such as in the creeping thistle Cirsium arvense ), tubers, bulbs, corms, and rhizomes. Vegetative reproduction has long been exploited in horticulture and agriculture, with various methods employed to multiply stocks of plants.

  wall pressure in plants, the mechanical pressure exerted by the cell contents against the cell wall. The rigidity (turgor) of a plant often depends on the level of wall pressure found in the cells of the stem. Wall pressure falls if the plant cell loses water.

  wilting loss of rigidity ( turgor) in plants, caused by a decreasing wall pressure within the cells making up the supportive tissues. Wilting is most obvious in plants that have little or no wood.

  wood hard tissue beneath the bark of many perennial plants; it is composed of water-conducting cells, or secondary xylem, and gains its hardness and strength from deposits of lignin.

  xerophyte plant adapted to live in dry conditions. Common adaptations to reduce the rate of transpiration include a reduction of leaf size, sometimes to spines or scales; a dense covering of hairs over the leaf to trap a layer of moist air (as in edelweiss); water storage cells; sunken stomata; and permanently rolled leaves or leaves that roll up in dry weather (as in marram grass). Many desert cacti are xerophytes.

  xylem tissue found in vascular plants, whose main function is to conduct water and dissolved mineral nutrients from the roots to other parts of the plant.

  Further Reading

  Attenborough, David The Private Life of Plants (1995)

  Bell, Adrian Plant Form. An Illustrated Guide to Flowering Plant Morphology

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  Biology

  A Self-Teaching Guide

  • Steven D. Garber(Author)
  • 2020(Publication Date)
  • Jossey-Bass

    (Publisher)

  leaves” because of a lack of better terminology.

  Figure 20.1

  Moss, illustrating rhizoids, leafy gametophytes, and attached sporophytes. The same plant has sporophyte and gametophyte generation (sporophyte grows from the gametophyte).

  VASCULAR PLANTS

  Some of the earliest known vascular plants had roots that functioned as holdfasts and absorbed water. They also had vascular tissue for water and nutrient movement. This tissue also provided strength and helped hold the plant up in the air. In addition, these early vascular plants had a waxy cuticular layer covering the leaves for water retention. The fossil record indicates there was a trend toward the reduction of the gametophyte generation in favor of the more dominant sporophyte generation, which contained the sporangia. The earliest vascular plants probably produced only one kind of spore from one kind of sporangium, a process called homospory. After germination, these spores developed into gametophytes with antheridia and archegonia. They produced the sperm and eggs, respectively. However, the trend toward heterospory (the production of two different kinds of spores) is also evident in the overall evolution of the vascular plants.

  Following the evolution of the aquatic vertebrates, which took place about 500 million years ago, the first vascular plants to colonize the land appear in the fossil record; at about the same time, some arthropods also began colonizing terrestrial habitats.

  A significant innovation unique to the vascular plants is the seed, which consists of an embryo and some stored food enclosed within a protective coat. The earliest known fossilized seeds date back 350 million years.

  Five major groups of tracheophytes, or vascular plants, are discussed below. To date, more than 260,000 species of vascular plants have been described.

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  BIOS Instant Notes in Plant Biology

  • Andrew Lack, David Evans(Authors)
  • 2021(Publication Date)
  • Taylor & Francis

    (Publisher)

  Section P - Spore-bearing vascular plants

  P1   EARLY EVOLUTION OF VASCULAR PLANTS

  Key Notes

  The earliest vascular plants

  Earliest fossils of land plants, Cooksonia, occur in late Silurian rocks. It had photosynthetic stems but no leaves or roots and no stomata. By early Devonian several genera occur. They were low growing plants less than 50 cm high bearing sporangia at the tips (Rhyniopsida), laterally (Zosterophyllopsida) or in bunches (Psilophyton). Aglaophyton may provide a link with bryophytes.

  Later developments

  There was rapid diversification through the Devonian era with developments of monopodial branching and trees belonging to the lycopsids, ferns and other living groups. Their greatest abundance was in the Carboniferous during which they reduced the CO2 levels by 10 times, cooling and drying the climate.

  Origins and evolution

  Compared with an aquatic environment, land plants require structures to withstand changes in temperature and humidity, wind, rain and desiccation. They require a conducting system for water and nutrients and mechanical strength. Spores are more resistant to desiccation than gametes so sporophytes become the main plant.

  Life cycle

  Fossils are of sporophytes with sporangia having no or limited dehiscence. Fossil gametophytes are little known, but some probable gametophyte fossils have cup-like structures at the stem tips bearing archegonia and antheridia.

  Homospory and heterospory

  Homosporous plants produce one type of spore that germinates to produce a hermaphrodite gametophyte; heterosporous plants have two types of spore, one producing only male gametophytes, the other female. Heterospory has evolved several times. Most early plants were homosporous but heterospory probably appeared early and increased during the Devonian.

  Related topics

  The bryophytes (O2)Clubmosses and quillworts (P2)

  Horsetails (P3) Ferns (P4)

  The earliest vascular plants

  Vascular plants first appeared probably in the Silurian era (Table 1 ). The oldest fossils are those of Cooksonia (Fig. 1 ) in the Rhyniopsida from late Silurian rocks, a little over 400 million years BP. Fossils of Cooksonia have been found in several places in Europe and North America. These plants had photosynthetic stems 5-8 cm high that branched dichotomously, i.e. into two even branches at each point, but no leaves or roots. Some had rhizomes, horizontal underground stems, and subterranean rhizoids, one cell thick, growing out from the rhizomes or stems that may have absorbed water and anchored the plant. The earliest fossil Cooksonia

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