The Seedless Vascular Plants: Ferns and Their Relatives

1. The Seedless Vascular Plants: Ferns and Their Relatives Chapter 21

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

3. Introduction • During early stages of vascular plant evolution: • Internal conducting tissue developed • True leaves appeared • Roots functioning in absorption and anchorage developed • Gametophytes became progressively smaller • 4 phyla of seedless vascular plants: Psilotophyta, Lycophyta, Equisetophyta, Polypodiophyta

4. Introduction • Psilotophyta • Sporophytes without true leaves or roots • Stems and rhizomes fork evenly • Lycophyta • Plants covered with microphylls - leaves with single vein whose trace not associated with leaf gap Psilotum Lycopodium

5. Introduction • Equisetophyta • Sporophytes with ribbed stems containing silica • Whorled, scalelikemicrophyllslacking chlorophyll • Polypodiophyta • Sporophytes with megaphylls- leaves with >1 vein and leaf trace associated with leaf gap • Often large and divided 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 • Lack leaves and roots

7. Phylum Psilotophyta – The Whisk Ferns • Structure and form cont’d.: • Sporophytes: • Enations - tiny, green, superficially leaflike, veinless, photosynthetic flaps of tissue • Roots, aided by mycorrhizal fungi, scattered along rhizomes

8. Phylum Psilotophyta – The Whisk Ferns • Reproduction: • Sporangia fused in 3s and produced at tips of short branches • Gametophytes develop from spores beneath ground • Branch dichotomously • No chlorophyll • Rhizoids aided by mycorrhizalfungi • Archegonia and antheridia scattered on surface • Zygote develops foot and rhizome • Rhizome separates from foot

9. Phylum Psilotophyta – The Whisk Ferns • Reproduction cont’d.:

10. Phylum Psilotophyta – The Whisk Ferns • Fossil whisk fern look-alikes • Silurian, 400mya • Cooksonia and Rhynia • Naked stems and terminal sporangia • Devonian, 400-350mya • Zosterophyllum • Naked stems and rounded sporangia along stem • Thought to be ancestral to club mosses

11. Phylum Lycophyta – The Ground Pines, Spike Mosses, and Quillworts • Collectively called club mosses • 2 living major genera • Lycopodium • Selaginella • 2 living minor genera • Several genera became extinct about 270mya • Sporophytes have microphylls • Have true roots and stems

12. Phylum Lycophyta • Lycopodium - ground pines • Often grow on forest floors • Stems simple or branched • Develop from branching rhizomes • Leaves usually < 1 cm long • Roots develop along rhizomes

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

14. Phylum Lycophyta • Lycopodiumreproduction cont’d.: Gametophyte

15. Phylum Lycophyta • Selaginella-spike mosses • Abundant in tropics • Branch more freely than ground pines • Leaves with liguleon upper surface

16. Phylum Lycophyta • Selaginellareproduction: • Produce 2 different kinds of gametophytes = heterospory • Microsporophylls bear microsporangia containing microsporocytes, producing tiny microspores - becomes male gametophyte, consisting ofantheridiumwithin microspore wall • Megasporophylls bear megasporangia containing megasporocytes, producing 4 large megaspores -develops into female gametophyte consisting of many cells inside megaspore • Several archegonia produced where spore wall ruptures

17. Phylum Lycophyta • Selaginellareproduction cont’d.:

18. Phylum Lycophyta • Isoetes-quillworts • Found in areas partially submerged in H2O for part of year • Microphylls arranged in tight spiral on stubby stem • Ligules occur towards leaf bases • Corms have vascular cambium • Plants generally > 10 cm tall

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

20. Phylum Lycophyta • Ancient relatives of club mosses and quillworts: • Dominant members of forests and swamps of Carboniferous, 325mya • 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 > 1.3 mtall • Stems jointed and ribbed • If branched, 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 H2O with xylem and phloem to outside • Vallecular canals - outside carinal canals contain air • Silica deposits on walls of stem epidermal cells

23. Phylum Equisetophyta

24. Phylum Equisetophyta • Equisetum reproduction: • Asexual by fragmentation of rhizomes • Sexual reproduction: • Strobili at tips of stems with sporangia connected tosporangiophores • Spores green with 4elaters attached • Gametophytes lobed, green, cushion-like, up to 8 mm in diameter Spores with elaters

25. Phylum Equisetophyta • Equisetumreproduction cont’d.:

26. Phylum Equisetophyta • Ancient relatives of horsetails: • Flourished in Carboniferous, 300mya • 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

27. Phylum Polypodiophyta – The Ferns • Structure and form: • Vary in size from tiny floating forms < 1 cm to giant tropical tree ferns up to 25 m tall • Fern leaves are megaphylls -fronds • Typically divided into smaller segments • Require external H2O for reproduction

28. Phylum Polypodiophyta – The Ferns • Reproduction: • Sporophyteconspicuous phase • Fronds, rhizomes, roots • Fronds first appear coiled in crozier, and unroll and expand • Fronds divided into segments called pinnae (singular: pinna) Crozier

29. Phylum Polypodiophyta – The Ferns • Reproduction cont’d.: • Sporangia stalked • 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 Sorus covered by indusium

30. Phylum Polypodiophyta – The Ferns • Reproduction cont’d.: • Meiosis forms spores in sporangia • Spores released and grow into gametophytes called prothalli(singular: prothallus) • Prothalli one cell thick, and have archegonia and antheridia • Zygote develops into young sporophyte • Gametophyte dies and leaves sporophyte growing independently

31. Phylum Polypodiophyta – The Ferns • Reproduction cont’d.:

32. Phylum Polypodiophyta – The Ferns • Fossil relatives of ferns: • Devonian, 375mya- possible ancestors of ferns • Resemble ferns in growth habit, but look more like whisk ferns Possible ancestors: Aglaophyton and Psilophyton

33. Phylum Polypodiophyta – The Ferns • Fossil relatives of ferns cont’d. • Carboniferous, 320-250mya - tree ferns abundant • Seeds found on some of fossil tree ferns

34. 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

35. 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