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Topic 5: seedless vascular plants (CH. 29) Vascular Plants (overview)

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  1. Vascular Plants (overview) – plants with xylem and phloem

    • 7 or 9 living phyla, depending on who you talk to

    • able to dominate most terrestrial habitats because of vascular tissues, waxy cuticle, and stomata

    • conducting tissues (xylem and phloem) called vascular tissues

      • cylindrical or elongated cells that form network throughout plant

      • xylem

        • xylem of all vascular plants includes tube-shaped cells that carry water and minerals up from roots

        • When functioning, these cells are dead, with only their walls providing a system of microscopic water pipes

        • typically at least partially lignified (having lignin, a highly branched polymer that makes cell wall more rigid)

      • phloem

        • transports carbohydrates, sugars, amino acids and other organic products in solution throughout plant (down and up)

        • living cells

  • roots, leavs and shoots

    • Roots :

      • Lignified vascular tissue also allowed the evolution of roots.

  • anchor vascular plants and enable them to absorb water and nutrients from the soil.

  • allow the shoot system to grow taller.

        • Leaves:

          • organs that increase the surface area of vascular plants, capturing more solar energy for photosynthesis

          • In terms of size and complexity, leaves can be classified as microphylls and megaphylls.

          • All lycophytes have microphylls, small leaves with only a single unbranched vein. These leaves probably evolved as small outgrowths on the surface of stems, supported by single strands of vascular tissue.

          • All other vascular plants have megaphylls, leaves with a highly branched vascular system.

            • A branched vascular system can deliver water and minerals to the expanded leaf.

            • can also export larger quantities of sugars from the leaf.

            • Megaphylls support more photosynthetic activity.

      • only with vascular tissue do you have true leaves, stems, and roots

    • sporophyte dominant

    • vascular tissue is usually only found in the sporophyte generation

    • seeds (when present) are highly resistant structures that increase ability of developing embryos to survive on land

    • divided into seedless and seed-forming groups; seed-forming phyla covered in future outlines

  1. Seedless Vascular Plants (ferns and fern allies)

    • sporophyte dominant and can grow independent of gametophyte in all

    • gametophyte small, reduced, but still able to grow independent of sporophyte in all

    • importance: dominated land during Carboniferous Period (354-290 million years ago), becoming a source of coal

      • coal is incompletely decomposed, highly compressed, carbon-rich rock derived mainly from the bodies of ancient seedless vascular plants (a type of “fossil fuel”)

      • fossil coal swamps are full of extinct plants

      • coal is a vital source of energy; burned for heat and for producing electricity (over half of U.S. electric production)

    • at least 3 extinct phyla represented in the fossil record; one will be covered, Phylum Rhyniophyta

    • New phylogenies define 2 phyla with living members – Lycophyta (club mosses, quillworts and spike mosses) and Pterophyta (ferns, horsetails and whisk ferns).

    • Older classification has 4 phyla. We use this for the course, and also for it to be consistent with your lab manuals. The textbook says otherwise.

      • Phylum Lycophyta

      • Phylum Pterophyta

      • Phylum Psilophyta (some group with Pterophyta; do fall in a clade with that group and Arthrophyta)

      • Phylum Arthrophyta (some group with Pterophyta; do fall in a clade with that group and Psilophyta)

  1. extinct Phylum Rhyniophyta – oldest vascular plant fossils (Cooksonia, 420 MYA)

    • branching axis; no leaves or roots

    • only a few centimeters tall

    • sporangia at ends of branches

    • appearance much like that of modern-day whisk ferns

    • homosporous – only one spore type, so only one gametophyte type

  1. Phylum Lycophyta – club mosses, quillworts and spike mosses

    • ~1000 living species; worldwide, but most in tropics and moist temperate regions; many species endangered

    • includes “resurrection plants”. What are they ?

    • fossil record includes tree-like forms that died out about 270 MYA

    • apparently evolved separately from the other seedless vascular plants

    • small, resembling mosses (but vascular with dominant sporophyte)

    • leafy stems usually less than 30 cm long

    • their leaves are also called microphylls, with very little vascular tissue (just a single vein); other vascular plant leaves have much more complex vascular tissue networks

    • homosporous and heterosporous genera

      • heterosporous – plant makes two types of meiospores, resulting in two types of gametophytes

      • megaspore is larger of the two; grows via mitosis into the female gametophyte

      • microspore is smaller of the two; grows via mitosis into the male gametophyte

    • sexual reproduction similar to that of ferns

    • sporangia grow from specialized leaves called sporophylls; sporophylls are clustered in a cone-like strobilus

  1. Phylum Pterophyta – ferns

    • somewhat complicated phylogeny; we will visit the tree of life in class to discuss this

    • fossils date to as long as 375 MYA (important fossil fuel source)

    • ~12,000 living species; throughout world, but ¾ of species tropical

    • most leafy, but some tree ferns

    • most are homosporous, but some are heterosporous

    • life cycle similar to moss except decreased gametophyte, independent and dominant sporophyte

      • gametophyte

        • germinating spore divides by mitosis and forms multicellular protonema

        • protonema grows into mature gametophyte called prothallus

          • typically heart-shaped; mostly one-cell thick

          • has rhizoids

      • gametes produced in male antheridia and female archegonia on same or separate prothalli

      • sperm made in antheridia swim to archegonia (using flagella; need outside water source to swim in)

      • sperm unites with egg, forming diploid zygote

      • zygote undergoes mitotic divisions and develops into sporophyte

        • sporophyte grows out gametophyte and takes over (larger, vascular, photosynthetic, responsible for all of own nutrition)

        • typically have horizontal, underground stem (rhizome)

        • leaves (called fronds) develop from rhizome as coiled “fiddleheads”

        • form stalked sporangia in clusters called sori, typically on the backs of fronds

      • spore mother cells in sporangium produce haploid spores

      • at maturity, outer covering of sporangium snaps off, catapulting spores

      • spore in right (mainly moist) environment will germinate

  1. Phylum Psilophyta – whisk ferns

    • probably form a monophyletic group with ferns and horsetails; some group these within the fern phylum

    • simplest living vascular plants

      • no true roots or leaves – leaf-like enations and such sometimes present

      • forking green stems (photosynthetic; true stems)

    • sexual reproduction much like ferns (have antheridia and archegonia, swimming sperm that need outside water, etc.)

    • all are homosporous

    • like ferns, sporophyte is dominant generation

    • gametophytes small, colorless

      • in soil beneath sporophytes

      • associated with fungi

      • saprobic or parasitic

      • some have elements of vascular tissue (only gametophytes known to have this)

    • tropical and subtropical

    • only 6 known living species

  1. Phylum Arthrophyta – horsetails (alternative phylum names: Sphenophyta; Equisetophyta)

    • probably form a monophyletic group with ferns and whisk ferns; some group these within the fern phylum

    • 15 known living species, all in genus Equisetum

    • most <1 m tall, some 3 m tall; widely scattered in damp regions throughout the world

    • fossil record back to 300 MYA

      • once much more diverse and dominant

      • fossil record includes tree-like forms as tall as 30 m

    • sporophyte dominant

      • branching underground rhizomes with roots at their nodes

      • hollow, ribbed, jointed, photosynthetic stems

      • whorls of scale-like, nonphotosynthetic leaves at nodes on stems

      • some have whorls of photosynthetic branches at nodes as well

      • stems hollow

      • silica deposits in some epidermal cells (stiffens; protects from predators)

      • some are called “scouring rushes” because they were used by pioneers for scrubbing dishes

    • most are homosporous

    • sexual reproduction similar to that of ferns

    • sporangia on underside of stalked structures called sporangiophores

    • sporangiophores are clustered in a cone-like strobilus at a stem tip


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