Download Topic 5: Seedless Vascular Plants (Ch. 29)

BIOL 1030 – TOPIC 5 LECTURE NOTES
TOPIC 5: SEEDLESS VASCULAR PLANTS (CH. 29)
I.
Vascular Plants (overview) – plants with xylem and phloem
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7 or 9 living phyla, depending on who you talk to
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able to dominate most terrestrial habitats because of vascular tissues, waxy cuticle, and stomata
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conducting tissues (xylem and phloem) called vascular tissues
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cylindrical or elongated cells that form network throughout plant
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xylem
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xylem of all vascular plants includes tube-shaped cells that carry water and minerals up from
roots
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When functioning, these cells are dead, with only their walls providing a system of microscopic
water pipes
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typically at least partially lignified (having lignin, a highly branched polymer that makes cell
wall more rigid)
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phloem
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transports carbohydrates, sugars, amino acids and other organic products in solution throughout
plant (down and up)
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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.
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BIOL 1030 – TOPIC 5 LECTURE NOTES
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A branched vascular system can deliver water and minerals to the expanded leaf.
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can also export larger quantities of sugars from the leaf.
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Megaphylls support more photosynthetic activity.
only with vascular tissue do you have true leaves, stems, and roots
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sporophyte dominant
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vascular tissue is usually only found in the sporophyte generation
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seeds (when present) are highly resistant structures that increase ability of developing embryos to
survive on land
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divided into seedless and seed-forming groups; seed-forming phyla covered in future outlines
II. Seedless Vascular Plants (ferns and fern allies)
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sporophyte dominant and can grow independent of gametophyte in all
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gametophyte small, reduced, but still able to grow independent of sporophyte in all
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importance: dominated land during Carboniferous Period (354-290 million years ago), becoming a
source of coal
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coal is incompletely decomposed, highly compressed, carbon-rich rock derived mainly from the
bodies of ancient seedless vascular plants (a type of “fossil fuel”)
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fossil coal swamps are full of extinct plants
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coal is a vital source of energy; burned for heat and for producing electricity (over half of U.S.
electric production)
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at least 3 extinct phyla represented in the fossil record; one will be covered, Phylum Rhyniophyta
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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.
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Phylum Lycophyta
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Phylum Pterophyta
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Phylum Psilophyta (some group with Pterophyta; do fall in a clade with that group and Arthrophyta)
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Phylum Arthrophyta (some group with Pterophyta; do fall in a clade with that group and Psilophyta)
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BIOL 1030 – TOPIC 5 LECTURE NOTES
III. extinct Phylum Rhyniophyta – oldest vascular plant fossils (Cooksonia, 420 MYA)
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branching axis; no leaves or roots
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only a few centimeters tall
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sporangia at ends of branches
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appearance much like that of modern-day whisk ferns
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homosporous – only one spore type, so only one gametophyte type
IV. Phylum Lycophyta – club mosses, quillworts and spike mosses
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BIOL 1030 – TOPIC 5 LECTURE NOTES
~1000 living species; worldwide, but most in tropics and moist temperate regions; many species
endangered
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includes “resurrection plants”. What are they ?
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fossil record includes tree-like forms that died out about 270 MYA
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apparently evolved separately from the other seedless vascular plants
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small, resembling mosses (but vascular with dominant sporophyte)
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leafy stems usually less than 30 cm long
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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
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homosporous and heterosporous genera
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heterosporous – plant makes two types of meiospores, resulting in two types of gametophytes
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megaspore is larger of the two; grows via mitosis into the female gametophyte
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microspore is smaller of the two; grows via mitosis into the male gametophyte
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sexual reproduction similar to that of ferns
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sporangia grow from specialized leaves called sporophylls; sporophylls are clustered in a cone-like
strobilus
V. Phylum Pterophyta – ferns
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somewhat complicated phylogeny; we will visit the tree of life in class to discuss this
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fossils date to as long as 375 MYA (important fossil fuel source)
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~12,000 living species; throughout world, but ¾ of species tropical
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most leafy, but some tree ferns
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most are homosporous, but some are heterosporous
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life cycle similar to moss except decreased gametophyte, independent and dominant sporophyte
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gametophyte
•
germinating spore divides by mitosis and forms multicellular protonema
•
protonema grows into mature gametophyte called prothallus
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typically heart-shaped; mostly one-cell thick
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has rhizoids
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BIOL 1030 – TOPIC 5 LECTURE NOTES
gametes produced in male antheridia and female archegonia on same or separate prothalli
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sperm made in antheridia swim to archegonia (using flagella; need outside water source to swim in)
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sperm unites with egg, forming diploid zygote
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zygote undergoes mitotic divisions and develops into sporophyte
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sporophyte grows out gametophyte and takes over (larger, vascular, photosynthetic, responsible
for all of own nutrition)
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typically have horizontal, underground stem (rhizome)
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leaves (called fronds) develop from rhizome as coiled “fiddleheads”
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form stalked sporangia in clusters called sori, typically on the backs of fronds
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spore mother cells in sporangium produce haploid spores
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at maturity, outer covering of sporangium snaps off, catapulting spores
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spore in right (mainly moist) environment will germinate
VI. Phylum Psilophyta – whisk ferns
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probably form a monophyletic group with ferns and horsetails; some group these within the fern phylum
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simplest living vascular plants
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BIOL 1030 – TOPIC 5 LECTURE NOTES
no true roots or leaves – leaf-like enations and such sometimes present
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forking green stems (photosynthetic; true stems)
sexual reproduction much like ferns (have antheridia and archegonia, swimming sperm that need outside
water, etc.)
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all are homosporous
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like ferns, sporophyte is dominant generation
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gametophytes small, colorless
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in soil beneath sporophytes
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associated with fungi
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saprobic or parasitic
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some have elements of vascular tissue (only gametophytes known to have this)
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tropical and subtropical
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only 6 known living species
VII. Phylum Arthrophyta – horsetails (alternative phylum names: Sphenophyta; Equisetophyta)
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probably form a monophyletic group with ferns and whisk ferns; some group these within the fern
phylum
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15 known living species, all in genus Equisetum
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most <1 m tall, some 3 m tall; widely scattered in damp regions throughout the world
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fossil record back to 300 MYA
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once much more diverse and dominant
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fossil record includes tree-like forms as tall as 30 m
sporophyte dominant
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branching underground rhizomes with roots at their nodes
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hollow, ribbed, jointed, photosynthetic stems
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whorls of scale-like, nonphotosynthetic leaves at nodes on stems
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some have whorls of photosynthetic branches at nodes as well
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stems hollow
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silica deposits in some epidermal cells (stiffens; protects from predators)
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some are called “scouring rushes” because they were used by pioneers for scrubbing dishes
most are homosporous
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BIOL 1030 – TOPIC 5 LECTURE NOTES
sexual reproduction similar to that of ferns
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sporangia on underside of stalked structures called sporangiophores
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sporangiophores are clustered in a cone-like strobilus at a stem tip
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