The Seedless Vascular Plants: Ferns and Their Relatives Chapter 21

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

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

Introduction Psilotophyta Sporophytes without true leaves or roots Psilotum 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 Lycopodium

Introduction Equisetophyta Sporophytes with ribbed stems containing silica Whorled, scalelike microphylls lacking chlorophyll Polypodiophyta Sporophytes with megaphylls - leaves with >1 vein and leaf trace associated with leaf gap Often large and divided Equisetum A fern

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

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

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 mycorrhizal fungi Archegonia and antheridia scattered on surface Zygote develops foot and rhizome Rhizome separates from foot

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

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

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 270 mya Sporophytes have microphylls Have true roots and stems

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

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

Phylum Lycophyta Lycopodium reproduction cont’d.: Gametophyte

Phylum Lycophyta Selaginella - spike mosses Abundant in tropics Branch more freely than ground pines Leaves with ligule on upper surface

Phylum Lycophyta Selaginella reproduction: Produce 2 different kinds of gametophytes = heterospory Microsporophylls bear microsporangia containing microsporocytes, producing tiny microspores - becomes male gametophyte, consisting of antheridium within 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

Phylum Lycophyta Selaginella reproduction cont’d.:

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

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

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

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

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

Phylum Equisetophyta

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 elaters attached Gametophytes lobed, green, cushion-like, up to 8 mm in diameter Spores with elaters

Phylum Equisetophyta Equisetum reproduction cont’d.:

Reconstruction of fossil giant horsetail, Calamites Phylum Equisetophyta Ancient relatives of horsetails: Flourished in Carboniferous, 300 mya 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

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

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

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

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

Phylum Polypodiophyta – The Ferns Reproduction cont’d.:

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

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

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

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