1. The Seedless Vascular Plants: Ferns and Their Relatives
Chapter 18
Lecture Outline
The Seedless Vascular Plants: Ferns and Their Relatives
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2. Outline Introduction Phylum Psilotophyta – The Whisk Ferns
Phylum Lycophyta – The Ground Pines, Spike Mosses and Quillworts
Phylum Equisetophyta – The Horsetails and Scouring Rushes
Phylum Polypodiophyta – The Ferns
Fossils

3. Introduction During early stages of vascular plant evolution:
Internal conducting tissue developed.
True leaves appeared.
Roots that function in absorption and anchorage developed.
Gametophytes became progressively smaller.
Four phyla of seedless vascular plants: Psilotophyta, Lycophyta, Equisetophyta, Polypodiophyta

4. Introduction Psilotophyta Lycophyta
Sporophytes have neither true leaves, nor roots.
Stems and rhizomes fork evenly.
Lycophyta
Plants covered with microphylls.
Microphylls - Leaves with single vein whose trace is not associated with a leaf gap
Psilotum
Lycopodium

5. Introduction Equisetophyta Polypodiophyta
Sporophytes have ribbed stems containing silica.
Have whorled, scalelike microphylls that lack chlorophyll
Polypodiophyta
Sporophytes have megaphylls that are often large and much divided.
Megaphylls - Leaves with more than one vein and a leaf trace associated with leaf gap
Equisetum
A fern

6. Phylum Psilotophyta – The Whisk Ferns
Resemble small, green whisk brooms
Structure and form:
Sporophytes:
Dichotomously forking stems
Above ground stems arise from rhizomes beneath surface of ground.
Have neither leaves nor roots
Enations along stems.
Enations - Tiny, green, superficially leaflike, veinless, photosynthetic flaps of tissue
Rhizoids, aided by mycorrhizal fungi, scattered along rhizomes.

7. Phylum Psilotophyta – The Whisk Ferns
Reproduction:
Sporangia fused in threes and produced at tips of short branches.
Gametophytes develop from spores beneath ground.
Branch dichotomously
No chlorophyll
Rhizoids aided by mycorrhizal fungi.
Archegonia and antheridia scattered on surface.
Zygote develops foot and rhizome.
Rhizome separates from foot.

8. Phylum Psilotophyta – The Whisk Ferns
Reproduction:

9. Phylum Psilotophyta – The Whisk Ferns
Fossil whisk fern look-alikes:
Silurian, 400 million years ago
Cooksonia and Rhynia
Naked stems and terminal sporangia
Devonian, million years ago
Zosterophyllum
Naked stems and rounded sporangia along stem
Thought to be ancestral to club mosses

10. Phylum Lycophyta – The Ground Pines, Spike Mosses, and Quillworts
Collectively called club mosses
Two living major genera
Lycopodium
Selaginella
Two living minor genera
Several genera that became extinct about 270 million years ago
Sporophytes have microphylls.
Have true roots and stems

11. Phylum Lycophyta Lycopodium - Ground pines Often grow on forest floors
Stems are simple or branched.
Develop from branching rhizomes
Leaves usually less than 1 cm long.
Roots develop along rhizomes.

12. Phylum Lycophyta Lycopodium reproduction:
Sporangia in axils of sporophylls.
Sporophyll - Sporangium-bearing leaves
In some species, sporophylls have no chlorophyll, are smaller than other leaves and clustered into strobili (singular: strobus).
In sporangia, sporocytes undergo meiosis, producing spores.

13. Phylum Lycophyta Lycopodium reproduction:
Spores grow into independent gametophytes.
In some species, gametophytes resemble tiny carrots, develop in the ground and are associated with mycorrhizal fungi.
In others, gametophytes develop on surface and are green.
Archegonia and antheridia produced on gametophytes.
Sperm are flagellated and water is essential for fertilization.

14. Phylum Lycophyta
Lycopodium reproduction:

15. Phylum Lycophyta Selaginella - Spike mosses
Especially abundant in tropics
Branch more freely than ground pines
Leaves have a ligule on upper surface.

16. Phylum Lycophyta Selaginella reproduction:
Produce two different kinds of gametophytes = heterospory.
Microsporophylls bear microsporangia containing microsporocytes, producing tiny microspores.
Microspore becomes male gametophyte, consisting of an antheridium within microspore wall.
Megasporophylls bear megasporangia containing megasporocytes, producing 4 large megaspores.
Megaspore develops into female gametophyte consisting of many cells inside megaspore.
Several archegonia produced where spore wall ruptures.

17. Phylum Lycophyta
Selaginella reproduction:

18. Phylum Lycophyta Isoetes - Quillworts
Most found in areas partially submerged in water for part of year.
Microphylls are arranged in a tight spiral on a stubby stem.
Ligules occur towards leaf bases.
Corms have vascular cambium.
Plants generally less than 10 cm tall.

19. Phylum Lycophyta Isoetes reproduction:
Similar to spike mosses, except no strobili
Sporangia at bases of leaves.

20. Surface of Lepidodendron, showing microphyll bases
Phylum Lycophyta
Ancient relatives of club mosses and quillworts:
Dominant members of forests and swamps of Carboniferous, 325 million years ago
Large, tree-like, up to 30 meters tall - Lepidodendron
Surface of Lepidodendron, showing microphyll bases

21. Phylum Equisetophyta – The Horsetails and Scouring Rushes
Equisetum
Branched and unbranched forms, usually less than 1.3 meters tall
Stems jointed and ribbed.
If branched, then branches in whorls.
Scalelike leaves in whorls at nodes.
Stomata in grooves between ribs.

22. Phylum Equisetophyta Stem anatomy:
Hollow central cavity from break down of pith
Two cylinders of smaller canals outside pith.
Carinal canals conduct water with xylem and phloem to outside.
Vallecular canals outside carinal canals contain air.
Silica deposits on walls of stem epidermal cells.

23. Phylum Equisetophyta Equisetum reproduction:
Asexual by fragmentation of rhizomes
Sexual reproduction:
Strobili at tips of stems with sporangia connected to sporangiophores.
Spores green with 4 ribbon- like elaters attached.
Aid in spore dispersal
Gametophytes lobed, green, cushionlike, up to 8 mm in diameter.
Spores with elaters

24. Phylum Equisetophyta
Equisetum reproduction:

25. Reconstruction of fossil giant horsetail, Calamites
Phylum Equisetophyta
Ancient relatives of horsetails:
Flourished in Carboniferous, 300 million years ago.
Human and ecological relevance:
Many giant horsetails used for food by humans and other animals.
Scouring rush stems used for scouring and sharpening.
Reconstruction of fossil giant horsetail, Calamites

26. Phylum Polypodiophyta – The Ferns
Structure and form:
Vary in size from tiny floating forms less than 1 cm to giant tropical tree ferns up to 25 m tall
Fern leaves are megaphylls - Referred to as fronds.
Typically divided into smaller segments
Require external water for reproduction

27. Phylum Polypodiophyta – The Ferns
Reproduction:
Sporophyte is conspicuous phase.
Fronds, rhizomes, roots
Fronds first appear coiled in crozier (fiddlehead), and then unroll and expand.
Fronds often divided into segments called pinnae (singular: pinna).
Crozier

28. Phylum Polypodiophyta – The Ferns
Reproduction:
Sporangia stalked.
May be scattered on lower leaf surface, confined to margins, or found in discrete clusters called sori (singular: sorus).
Sori may be protected by indusia (singular: indusium).
With row of heavy-walled, brownish cells = annulus
Annulus catapults spores out of sporangium.
Sorus covered by indusium

29. Phylum Polypodiophyta – The Ferns
Reproduction:
Meiosis forms spores in sporangia.
Spores released and grow into gametophytes called prothalli (singular: prothallus).
Prothalli are one cell thick, and have archegonia and antheridia.
Zygote develops into young sporophyte.
Gametophyte, or portion of it, dies and leaves sporophyte growing independently.

30. Phylum Polypodiophyta – The Ferns
Reproduction:

31. Phylum Polypodiophyta – The Ferns
Fossil relatives of ferns:
Devonian, 375 million years ago - Possible ancestors of ferns
Resemble ferns in growth habit, but look more like whisk ferns
Possible ancestors: Aglaophyton and Psilophyton

32. Phylum Polypodiophyta – The Ferns
Fossil relatives of ferns
Carboniferous, million years ago - Tree ferns abundant
Seeds found on some of fossil tree ferns.

33. Phylum Polypodiophyta
Human and ecological relevance:
House plants
Function well as air filters
Outdoor ornamentals
Cooked rhizomes as food
Folk medicine
Fronds used in thatching for houses.
Basketry and weaving

34. Fossils
A fossil - Any recognizable prehistoric organic object preserved from past geological ages.
Conditions of formation almost always include quick burial and an accumulation of sediments.
Hard parts more likely preserved than soft parts.

35. Fossils Molds, casts, compressions, and imprints:
After being buried in sediment and hardened into rock, organic material slowly washed away.
If air space remains - Mold
If silica fills space - Cast
Compression - Objects buried by layers of sediment and overlying sheer weight compresses them to thin film of organic material and an outline.
Image of an impression = imprint
Coal is a specific type of compression.
Compression fossil

36. Fossils
Petrifactions - Uncompressed rock-like material in which original cell structure has been preserved
Chemicals in solution infiltrate cells and cell walls, where they crystallize and harden, preserving original material.
Coprolites - Dung of prehistoric animals and humans
Unaltered fossils - Organisms fell into oil or water that lacked oxygen and did not permit decay.
Petrified wood

37. Review Introduction Phylum Psilotophyta – The Whisk Ferns
Phylum Lycophyta – The Ground Pines, Spike Mosses and Quillworts
Phylum Equisetophyta – The Horsetails and Scouring Rushes
Phylum Polypodiophyta – The Ferns
Fossils