Download Life: The Science of Biology, 8e

Chapter 28 - Sadava
Plants without Seeds:
from Water to Land
Before we start Plants, a review….
 Domain Archaea
 Prokaryotic, include extremophile bacteria
 Domain Bacteria
 Prokaryotic, includes what we knew as Kingdom
Monera
 Domain Eukarya
 Eukaryotic
 Includes:
 Kingdom Fungi
 What we knew as Kingdom Protista (green algae are
related to plants)
 Kingdom Plantae
 Kingdom Animalia
Land plants are monophyletic
 all descend from a single common
ancestor
 One shared derived character
 a synapomorphy
 development from an embryo protected
by tissues of the parent plant
 Why is this important on land?
 Also called embryophytes
Land plants retain derived features they
share with green algae (which are
protists):
 Chlorophyll a and b.
 Starch as a storage product.
 Cellulose in cell walls.
Photo 28.2 Green algae of
phylum Chlorophyta are most
likely ancestors of plants.
“Plants” can be defined in several ways
 Streptophytes include land plants and a
paraphyletic group of green algae —all retain
egg within parent’s body
 Green plants: streptophytes plus all other
green algae. All have chlorophyll b
 This textbook: “plants” refers only to land
plants
 What we think of in Kingdom Plantae
10 clades of land plants
 Vascular plants, or tracheophytes
 7 clades
 all have conducting cells called tracheids
 The seven groups of vascular plants
constitute a clade themselves
 Nonvascular plants
 3 clades
www.sonoma.edu/users/c/cannon/
Plants first appeared on land between 400–500
million years ago
 Adaptations were needed to survive in dry
environments
 Large plants must transport water to all parts
of plant
 Needed support in air
 Needed methods to disperse gametes
Characteristics of land plants:
 The cuticle (waxy lipids)
 Stomata – openings in stems and leaves;





regulate gas exchange (except liverworts)
Gametangia enclosing gametes
Embryos in a protective structure
Pigments that protect against UV radiation
Spore walls containing sporopollenin
Mutualistic relationships with fungi to promote
nutrient uptake from soil
Alternation of generations
All land plants have a life
cycle with alternation of
generations
 multicellular haploid
(gametophyte)
 multicellular diploid
(sporophyte) individuals
Alternation of generations
 Sporophyte
 Produces spores, all cells are diploid
 Cells in sporangia (in sporophyte) undergo
meiosis to produce haploid, unicellular
spores
 Spores are released
 Spore develops into multicellular haploid
structure, the gametophyte
 Gametophyte
 Produces gametes, all cells are haploid
 Produce gametes by mitosis
 Fusion of egg and sperm results in diploid
zygote
 Zygote develops into sporophyte
Reduction of the gametophyte generation is a
major theme in plant evolution
 In nonvascular plants: gametophyte is larger,
longer-lived, and more self-sufficient than the
sporophyte
 Gametophyte is photosynthetic
 In plants that appeared later, this is reversed
 In seed vascular plants (gymnosperms and
angiosperms), sporophyte generation is
dominate
 Sporophyte is photosynthetic
 Gametophyte might only be a few cells it is so
small
Nonvascular plants
 Do not have vascular tissue
 liverworts, hornworts, and mosses
 These groups do not form a clade – why?
In nonvascular plants, the
gametophyte generation
is photosynthetic
Sporophytes arising
from gametophytes
 Sporophytes may or may
not be photosynthetic,…
 but are always
nutritionally dependent
on gametophyte, and is
permanently attached
Gametophytes
http://taggart.glg.msu.edu/bot335/MOSS.GIF
Haploid gametophyte produces gametes in
specialized sex organs (gametangia)
 Female: archegonium  produces one egg
 Male: antheridium  produces many sperm
with two flagella each
Flagellated moss sperm
http://www.dkimages.com/discover/prev
iews/832/20113674.JPG
Archegonium
Antheridium
• Nonvascular plants
• Sperm must swim to
archegonium, or be
splashed by raindrops
• Egg or archegonium
releases chemical
attractants for sperm
• Water is required for
all these events
Vascular Plants
• Vascular plants include the club mosses, ferns,
conifers, and angiosperms (flowering plants).
• True roots and leaves
What Features Distinguish the Vascular
Plants?
The vascular system consists of tissue
specialized for transport of materials
 Xylem
 conducts water and minerals from soil up
to aerial parts of plant.
 Some cells have lignin — provides support
 Phloem
 conducts products of photosynthesis
through plant.
http://plantandsoil.unl.edu/croptechnology2005/UserFiles/Image/siteImages/Fig-3-large.gif
 Tracheids are main
water-conducting
element in xylem
 Evolution of tracheids in
plants set stage for
invasion of land
First plant fossils are from
Silurian (408-440 mya)
 Made land more
hospitable for animals
 Amphibians and insects
arrived soon after plants
www.unlv.edu/Colleges/Sciences/Biology/
Schulte/Anatomy/CellsTissues
Vascular plants also have a
large, branching,
independent sporophyte
 Mature sporophyte is
nutritionally independent
from gametophyte
Fern
prothallus
Small independent gametophyte (left) and
branched sporopythe (right) of ferns
http://virtual.yosemite.cc.ca.us/randerson/Lynn's%20Bioslides/20.jpg
http://web.cortland.edu/broyles/hayg
• Vascular plants
• Euphyllophytes
• “true leaf plants”
• Includes:
• Monilophytes – seedless vascular plants that have
megaphylls
• seed plants (gymnosperms and flowering plants)
• Synapomorphies include overtopping growth
— new branches grow beyond the others —an
advantage in the competition for light
True leaves evolved
 flattened photosynthetic structures arising
from a stem or branch
 has true vascular tissue
 two types
 Microphylls – small, one vascular strand
 Club mosses have these
 Megaphylls
Heterosporous vascular plants produce
two types of spores:
 Megaspores develop into female
gametophytes — megagametophyte
 Megaspores are produced in small
numbers in megasporangia
 Microspores develop into male
gametophytes — microgametophyte
 Microspores are produced in large
numbers in microsporangia
Nonvascular seedless land plants: three
clades:
 liverworts
 mosses
 hornworts
Embryophytes
Nonvascular Seedless plants
Hepatophyta
Liverworts: Hepatophyta
 Sporophytes very short
 Remember that gametophyte generation is
dominant in nonvascular plants
 Can reproduce asexually
 Do so by dispersing gemmae which are in
gemmae cups
www.bcbiodiversity.homestead.com/files
Embryophytes
Nonvascular Seedless plants
Bryophyta
The mosses: Bryophyta
 Mosses (plus hornworts and vascular plants)
have stomata important in water & gas
exchange
Embryophytes
Nonvascular Seedless plants
Anthocerophyta
Hornworts: Anthocerophyta
 Gametophytes are flat plates of cells
 Have stomata, which do not close
http://www.botany.org/PlantImages/Conant/CA06-014_300.jpg
Seedless Vascular Plants
Seedless VASCULAR
plants – three
monophyletic
clades:
 club mosses
 horsetails
 whisk ferns
 plus ferns and
allies (not
monophyletic,
though 97% are)
Seedless Vascular Plants
Seedless vascular plants
 Small, short-lived
gametophyte is
independent of the large
sporophyte
 Single-celled spore is
resting stage
 Can grow larger because
of vascular tissue but
must have water for part
of life cycle — for the
flagellated, swimming
sperm
www.biologie.uni-hamburg.de/b-online/library/webb/BOT311/FERNS
Embryophytes
Seedless Vascular Plants
Lycophytes
Lycophytes: club mosses, spike mosses, and
quillworts
 Roots and stems have dichotomous
branching
 Leaves are microphylls
 Strobilli – clusters of sporangia
Lycopodium annotinum
http://ip30.eti.uva.nl/bis/flora/pictures
Embryophytes
Seedless Vascular
Euphyllophytes
Monilophytes
Monilophytes (a.k.a. Pteridophytes) — horsetails,
whisk ferns, and ferns & allies, form a clade
 Horsetails and whisk ferns are both monophyletic,
but ferns are not
 But 97% of ferns form a clade — the
leptosporangiate ferns
Embryophytes
Seedless Vascular
Euphyllophytes
Monilophytes
Horsetails
 15 species in one
genus — Equisetum
 Silica in cell walls —
“scouring rushes”…
used for cleaning
Equisetum hymale
www.plantoftheweek.org/image
Embryophytes
Seedless Vascular
Euphyllophytes
Monilophytes
Whisk ferns
 15 species in two
genera
 No roots but welldeveloped vascular
system
Psilotum nudum
http://www.botanik.uni-karlsruhe.de/garten/fotos-knoch/Psilotum%20nudum%20Gabelblatt%201.jpg
Embryophytes
Seedless Vascular
Euphyllophytes
Monilophytes
 Sporangia occur on undersides of leaves in
clusters called sori
http://departments.bloomu.edu/biology
/pics/botany/fern_sori2w.jpg
Monilophytes (Pteridophytes) – Ferns
 Fern gametophytes produce antheridia and
archegonia, not always at same time or on
same gametophyte
www.esu.edu/~milewski/intro_biol_two/lab_2_moss_ferns
Embryophytes
Seedless Vascular
Euphyllophytes
Monilophytes
Most ferns found in shaded, moist environments
 Tree ferns can reach heights of 20 m
Dixie Woods fern,
Dryopteris australis
Tree ferns
http://www.we-du.com/images/plants/350/frndrydwf.jpg
http://www.wettropics.gov.au/st/rainforest_expl
orer/Resources/Images/plants/TreeFerns.jpg