Transcript Chapter 18
Chapter 18 Lecture Outline The Seedless Vascular Plants: Ferns and Their Relatives Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 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 Introduction Psilotophyta • Sporophytes have neither true leaves, nor roots. • Stems and rhizomes fork evenly. Psilotum Lycophyta • Plants covered with microphylls. – Microphylls - Leaves with single vein whose trace is not associated with a leaf gap Lycopodium Introduction Equisetophyta • Sporophytes have ribbed stems containing silica. • Have whorled, scalelike microphylls that lack chlorophyll Equisetum 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 A fern Phylum Psilotophyta – The Whisk Ferns Resemble small, green whisk brooms Structure and form: • Sporophytes: – Dichotomously forking stems o Above ground stems arise from rhizomes beneath surface of ground. – Have neither leaves nor roots – Enations along stems. o Enations - Tiny, green, superficially leaflike, veinless, photosynthetic flaps of tissue – Rhizoids, aided by mycorrhizal fungi, scattered along rhizomes. 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. Phylum Psilotophyta – The Whisk Ferns Reproduction: Phylum Psilotophyta – The Whisk Ferns Fossil whisk fern look-alikes: • Silurian, 400 million years ago – Cooksonia and Rhynia o Naked stems and terminal sporangia • Devonian, 400-350 million years ago – Zosterophyllum o Naked stems and rounded sporangia along stem o Thought to be ancestral to club mosses 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 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. 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. 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. Phylum Lycophyta Lycopodium reproduction: Phylum Lycophyta Selaginella - Spike mosses • Especially abundant in tropics • Branch more freely than ground pines • Leaves have a ligule on upper surface. Phylum Lycophyta Selaginella reproduction: • Produce two different kinds of gametophytes = heterospory. – Microsporophylls bear microsporangia containing microsporocytes, producing tiny microspores. o – Microspore becomes male gametophyte, consisting of an antheridium within microspore wall. Megasporophylls bear megasporangia containing megasporocytes, producing 4 large megaspores. o Megaspore develops into female gametophyte consisting of many cells inside megaspore. o Several archegonia produced where spore wall ruptures. Phylum Lycophyta Selaginella reproduction: 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. Phylum Lycophyta Isoetes reproduction: • Similar to spike mosses, except no strobili • Sporangia at bases of leaves. 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 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. 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. 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 ribbonlike elaters attached. o – Aid in spore dispersal Gametophytes lobed, green, cushionlike, up to 8 mm in diameter. Spores with elaters Phylum Equisetophyta Equisetum reproduction: 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 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. o – Typically divided into smaller segments Require external water for reproduction Phylum Polypodiophyta – The Ferns Reproduction: • Sporophyte is conspicuous phase. – Fronds, rhizomes, roots – Fronds first appear coiled in crozier (fiddlehead), and then unroll and expand. o Fronds often divided into segments called pinnae (singular: pinna). Crozier 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). o Sori may be protected by indusia (singular: indusium). With row of heavy-walled, brownish cells = annulus o Annulus catapults spores out of sporangium. Sorus covered by indusium 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. Phylum Polypodiophyta – The Ferns Reproduction: 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 Phylum Polypodiophyta – The Ferns Fossil relatives of ferns • Carboniferous, 320-250 million years ago - 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 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. 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 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 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