Transcript chapter_21_lecture

Chapter 21
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
–
Roots, 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