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

 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.

1 of 7 BIOL 1030 – TOPIC 5 LECTURE NOTES  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

II. 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)

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III. 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

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

3 of 7 BIOL 1030 – TOPIC 5 LECTURE NOTES  ~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

V. 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

4 of 7 BIOL 1030 – TOPIC 5 LECTURE NOTES  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

VI. Phylum Psilophyta – whisk ferns

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

 simplest living vascular plants

5 of 7 BIOL 1030 – TOPIC 5 LECTURE NOTES  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

VII. 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

6 of 7 BIOL 1030 – TOPIC 5 LECTURE NOTES  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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