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The Plant Kingdom:
Seedless Vascular Plants
Chapter 23
Artist’s conception of a tropical Carboniferous forest.
During the Carboniferous period, North America and Europe
were considerably closer to the equator than they are today
and had tropical swamp forests. Carboniferous forests in drier
regions farther away from the equator were sparser and more
open than the one depicted here.
Lygodium overtaking cypress in Florida.
LEARNING OBJECTIVE 1
•
Summarize the features that
distinguish seedless vascular plants
from bryophytes
KEY TERMS
•
XYLEM
•
•
Vascular tissue that conducts water and
dissolved minerals
PHLOEM
•
Vascular tissue that conducts dissolved sugar
and other organic compounds
Seedless Vascular Plants
•
Adaptations that bryophytes lack
•
•
•
Vascular tissues (xylem and phloem)
Dominant sporophyte generation
As in bryophytes, reproduction depends
on water to transport motile sperm cells
Tasmanian Tree Fern
Evolution of
Seedless Vascular Plants
SEEDLESS VASCULAR PLANTS
B
Seed plants
Ferns
Whisk ferns
Horsetails
FERNS
Club mosses
Spike mosses
Quillworts
LYCOPHYTES
Evolution
of seeds
Evolution of
microphylls
Evolution of
megaphylls
A
Ancestral
vascular
plant
Fig. 23-2, p. 447
LEARNING OBJECTIVE 2
•
Contrast microphylls and megaphylls
KEY TERMS
•
•
MICROPHYLL
•
Type of leaf found in lycophytes
•
Contains one vascular strand
MEGAPHYLL
•
•
Type of leaf found in virtually all vascular
plants except lycophytes
Contains multiple vascular strands
True Leaves
•
Two basic types of true leaves,
microphylls and megaphylls, evolved
independently of each other
Evolution of Leaves
Stem
Microphyll
Vascular
tissue
Enation
Vein
Smooth
stem
Enation
Vascular
supply to
enation
(a) Microphyll evolution
Microphyll
(one vein)
Thicker
main Dichotomous
Equal stem end branches
branches
Vascular
tissue
Thinner
side
branch
Overtopping
Dichotomously
(unequal
branching stems
branching)
(b) Megaphyll evolution
Planation
(branching in
same plane)
Webbing of side
Megaphyll
branch system (many veins)
Fig. 23-3, p. 448
Stem
Vascular
tissue
Microphyll
Enation
Vein
Smooth
Enation
Vascular
stem
supply to
(a) Microphyll evolution
enation
Thicker
main Dichotomous
stem end branches
Equal
branches
Vascular
tissue
Microphyll
(one vein)
Thinner
side
branch
Overtopping
Dichotomously
(unequal
branching stems
branching)
(b) Megaphyll evolution
Planation
(branching in
same plane)
Webbing of side
branch system
Megaphyll
(many veins)
Stepped Art
Fig. 23-3, p. 448
LEARNING OBJECTIVE 3
•
Distinguish between the two phyla of
seedless vascular plants
KEY TERMS
•
FERNS (phylum Pteridophyta)
•
•
•
•
Phylum of seedless vascular plants that
reproduce by spores produced in sporangia
Undergoes alternation of generations
between dominant sporophyte and
gametophyte (prothallus)
Largest, most diverse group of seedless
vascular plants
Whisk ferns and horsetails classified as ferns
KEY TERMS
•
LYCOPHYTES (phylum Lycopodiophyta)
•
•
Phylum of seedless vascular plants, some of
which are heterosporous
Lycophytes include club mosses, spike
mosses, quillworts
Fern Diversity
Fern Diversity
Fern Diversity
Fern Diversity
LEARNING OBJECTIVE 4
•
Name and briefly describe ferns
•
Explain why whisk ferns and horsetails
are currently classified as ferns
Fern Sporophytes 1
•
Consist of
•
•
•
A rhizome that bears fronds (megaphylls)
True roots
Whisk fern sporophytes
•
•
Have dichotomously branching rhizomes
and erect stems
Lack true roots and leaves
Fern Sporophytes 2
•
Horsetail sporophytes
•
•
Roots, rhizomes, and aerial stems are hollow
and jointed
Leaves are reduced megaphylls
Classification
•
Whisk ferns and horsetails were
considered distinct enough to be classified
in separate phyla
•
DNA comparisons and similarities in
sperm structure resulted in reclassification
as ferns
Whisk Fern
Sporangia
Aerial stem
with scale-like
outgrowths
(no leaves)
Fig. 23-9a, p. 452
Whisk Fern
Antheridia
Archegonia
Rhizoids
(b) The gametophyte of P. nudum lives
underground, nourished by mycorrhizae.
Fig. 23-9b, p. 452
Ancient Horsetail
Horsetails
Strobilus
Reproductive
shoot
Vegetative
shoot
(a) In some horsetail (Equisetum) species,
both fertile shoots, which bear conelike strobili,
and vegetative (nonreproductive) shoots are
unbranched.
Fig. 23-11a, p. 453
Horsetail Spores
Spore
Elater
Fig. 23-12b, p. 456
LEARNING OBJECTIVE 5
•
Describe the life cycle of ferns
•
Compare their sporophyte and
gametophyte generations
Life Cycle of Ferns 1
•
Fern fronds bear sporangia in clusters
(sori)
•
•
Meiosis in sporangia produces haploid spores
Fern gametophyte (prothallus) develops
from a haploid spore
•
Bears both archegonia and antheridia
Life Cycle of Ferns 2
•
Each archegonium contains a single,
nonmotile egg; each antheridium produces
numerous sperm cells
•
Following fertilization, diploid zygote grows
by mitosis into a multicellular embryo
(immature sporophyte)
Animation: Fern Life Cycle
CLICK
TO PLAY
Fern Life Cycle
Underside of enlarged
mature gametophyte
(prothallus)
Germination of spores
and development of
young gametophyte
Egg
5
4
Spores
released
Rhizoids
3
Antheridium
Sporangium
Meiosis
Sorus 2
(cluster of
sporangia)
Archegonium
HAPLOID (n)
GAMETOPHYTE
GENERATION
Cells within
sporangia undergo
meiosis
Sperm cell
Fertilization
DIPLOID (2n)
SPOROPHYTE
GENERATION
Frond
Zygote
6
1
Leaf of young
sporophyte
Leaf cross section
Haploid
prothallus
Fiddlehead
Roots
Underside of
a frond
Fern
(mature
sporophyte)
Development of
the sporophyte
Rhizome
Root of young
sporophyte
Fig. 23-5, p. 450
Fiddleheads
Sori
Prothallus
Archegonium
Rhizoids
Fig. 23-8, p. 451
LEARNING OBJECTIVE 6
•
Name and briefly describe the three
groups of lycophytes
3 Groups of Lycophytes
1. Club moss sporophyte
•
•
•
true roots
rhizomes and erect or trailing aerial stems
small, scalelike microphylls
Club Mosses
Strobilus
Leaves
(microphylls)
(a) The sporophyte of Lycopodium obscurum
has small, scalelike, evergreen leaves
(microphylls). Spores are produced in
sporangia on fertile leaves clustered in a
conelike strobilus.
(b) Vegetative growth of Lycopodium
complanatum, which has a creeping growth
form. Like most club mosses, L. complanatum
prefers moist, shady woodlands.
Fig. 23-14, p. 457
3 Groups of Lycophytes
2. Spike moss sporophyte
•
•
•
long, creeping rhizomes that typically branch
dichotomously
roots that branch dichotomously
overlapping, scalelike microphylls
Spike Moss
Resurrection Plant
3 Groups of Lycophytes
3. Quillwort sporophyte
•
•
•
underground corm
cylindrical, quill-like microphylls
roots
Quillworts
LEARNING OBJECTIVE 7
•
Compare the generalized life cycle of a
homosporous plant with that of a
heterosporous plant
KEY TERMS
•
HOMOSPORY
•
•
Production of one type of n spore that gives
rise to a bisexual gametophyte
HETEROSPORY
•
Production of two types of n spores,
microspores and megaspores
KEY TERMS
•
MICROSPORE
•
•
The n spore in heterosporous plants that
gives rise to a male gametophyte that
produces sperm cells within antheridia
MEGASPORE
•
The n spore in heterosporous plants that
gives rise to a female gametophyte that
produces eggs within archegonia
Life Cycle: Heterosporous Plants
Gametophyte
Megaspore
Microspore
Meiosis
Antheridium
HAPLOID (n)
GAMETOPHYTE
GENERATION
DIPLOID (2n)
SPOROPHYTE
GENERATION
Microspore mother cell
Megaspore
mother cell
Archegonium
Gametophyte
Sperm
Egg
Fertilization
Zygote
Microsporangium
Embryo
Megasporangium
Sporophyte
Fig. 23-17, p. 459
Life Cycle: Selaginella
Male gametophyte
develops inside
microspore wall
3
Single antheridium in male
gametophyte produces many
sperm cells
2
Microspores
5
Sperm cell
Ruptured
Archegonium
megaspore wall
containing egg
Female gametophyte
develops and protrudes
4
from megaspore wall
Longitudinal
section through
Megaspores
archegonium
Egg
HAPLOID (n)
GAMETOPHYTE
GENERATION
Meiosis
Fertilization
Microsporangium
DIPLOID (2n)
with microspore
SPOROPHYTE
mother cells
GENERATION
Female
Megasporangium
with megaspore
Strobilus gametophyte
mother cells
First
1
leaves
Leaf
(microphyll)
Stem
Zygote
Stem
Longitudinal section
6
Root
through strobilus
Root
Young sporophyte
Mature
(attached to female
sporophyte
gametophyte)
Fig. 23-18, p. 460
LEARNING OBJECTIVE 8
•
Name and describe one of Earth’s
earliest vascular plants
Oldest Vascular Plants
•
Phylum Rhyniophyta
•
According to fossil record, arose about 420
mya and became extinct about 380 mya
Early Vascular Plant
•
Rhynia gwynne-vaughanii
•
•
•
•
•
Superficially resembled whisk ferns
Leafless upright stems branched
dichotomously from an underground rhizome
Lacked roots, but had absorptive rhizoids
Sporangia formed at ends of short branches
Internal structure of rhizome contained a
central core of xylem cells for conducting
water and minerals
Rhynia gwynne-vaughanii
Aglaophyton major
LEARNING OBJECTIVE 9
•
Describe the ecological and economic
significance of the ferns and
lycophytes
Ecology and Economics 1
•
Ferns and lycophytes help form soil, prevent
erosion
•
•
Branching underground rhizomes and roots or
rhizoids hold soil in place
Living species of limited economic importance
•
Many cultivated for aesthetic appeal
Ecology and Economics 2
•
Coal deposits
•
•
Formed from remains of ancient ferns, club
mosses, horsetails
Powered Industrial Revolution of 19th century,
used today to produce electricity