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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.
Lycophyta• Plants covered with
microphylls.– Microphylls - Leaves with
single vein whose trace is not associated with a leaf gap
Psilotum
Lycopodium
Introduction Equisetophyta
• 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
Phylum Psilotophyta – The Whisk Ferns
Structure and form:• Sporophytes:
– Dichotomously forking stemso 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.
Resemble small, green whisk brooms
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 stemo 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
• 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.
Lycopodium reproduction:
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 ribbon-like 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 = annuluso 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