LECTURE 2 Land Plant Diversity Liverwortsassets.openstudy.com/updates/attachments/4eff4a57e... ·...
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LECTURE 2
Land Plant Diversity
Liverworts
Systematics -A science that includes and
encompasses traditional taxonomy, the description,
identification, nomenclature, and classification of
organisms, and that has as its primary goal the
reconstruction of phylogeny, or evolutionary history of
life. (M. G. Simpson 2006)
Taxonomy - The theory and practice encompassing
description, identification, nomenclature and
classification of groups of organisms (species, genera,
etc.)
-Does not necessarily include phylogeny
Monophyletic taxon: A group composed of a collection of
organisms, including the most recent common ancestor of
all those organisms and all the descendants of that most
recent common ancestor. A monophyletic taxon is also
called a clade.
O X X X X X X XO X Y X X X G X
O Y X X Y X G G
GREEN PLANT - PHYLOGENY
(Simpson 2006; pg. 52)
GREEN PLANT SYNAPOMORPHIES
1) Chlorophyll b
2) Thylakoids Stacked
Into Grana
3) True Starch Storage
Chemical structure Chloroplasts in cells of
Elodea
Chloroplast
GREEN PLANTS - PHYLOGENY
LIFE CYCLE - ALTERNATION OF GENERATIONS
LIFE CYCLE – (NOT) ALTERNATION OF GENERATIONS
animals
ISOGAMY and ANISOGAMY
OOGAMY
GREEN PLANTS - PHYLOGENY
PLASMODESMATA- Canals interconnecting cells allowing for
transportation of molecules.
Coleochaete
Chara
GREEN ALGAE -
Most closely
related to the land
plants.
Both DNA and
morphological data
agree.
THE MOVE TO LAND
Landplant Adaptations:
1) Physically survive out of water: Avoid desiccation? Water
transport as plants get larger?
2) Sexual reproduction: Algae have free swimming sperm,
how does sperm get to egg on land?
LAND PLANT PHYLOGENY
(from Simpson 2006)
Landplant Synapomorphies:
1) Retention of Embryo on Gametophyte: Embryo is formed
on gametophyte of Charophytes and Coleochaete but
released.
2) Sporangium: A multicellular structure that protects and
produces spores through meiosis
3) Cuticle: A protective layer secreted by epidermal plant
cells for protection against desiccation. A transparent
layer of cutin, a polymer of fatty acids.
4) Antheridium (“male” gametangium): A multicellular
structure that produces and protects the sperm
5) Archegonium (“female” gametangium): A multicellular
structure that produces and protects the egg
2) Sporangium: A multicellular structure that protects and
produces spores through meiosis
Sphagnum Moss
(1N)
Landplant Synapomorphies:
1) Retention of Embryo on Gametophyte: Embryo is formed
on gametophyte of Charophytes and Coleochaete but
released.
2) Sporangium: A multicellular structure that protects and
produces spores through meiosis
3) Cuticle: A protective layer secreted by epidermal plant
cells for protection against desiccation. A transparent
layer of cutin, a polymer of fatty acids.
4) Antheridium (“male” gametangium): A multicellular
structure that produces and protects the sperm
5) Archegonium (“female” gametangium): A multicellular
structure that produces and protects the egg
3) Cuticle: A protective layer secreted by epidermal plant
cells for protection against desiccation. A transparent
layer of cutin, a polymer of fatty acids.
Cuticle
Epiderma
l leaf
cells
Landplant Synapomorphies:
1) Retention of Embryo on Gametophyte: Embryo is formed
on gametophyte of Charophytes and Coleochaete but
released.
2) Sporangium: A multicellular structure that protects and
produces spores through meiosis
3) Cuticle: A protective layer secreted by epidermal plant
cells for protection against desiccation. A transparent
layer of cutin, a polymer of fatty acids.
4) Antheridium (“male” gametangium): A multicellular
structure that produces and protects the sperm
5) Archegonium (“female” gametangium): A multicellular
structure that produces and protects the egg
4) Antheridium (“male” gametangium): A multicellular
structure that produces and protects the sperm (male
gametes)
5) Archegonium (“female” gametangium): A multicellular
structure that produces and protects the egg (female
gamete)
A
B
antheridium archegonium
EXAMPLE FROM MOSS
Egg
kneck
cells
moss
gametophyte
Bryophytes
BRYOPHYTES - Paraphyletic
(From Simpson 2006)
BRYOPHYTES - Characteristics unique from other land
plants
1) Gametophyte Dominant- The predominant vegetative
form is the gametophyte phase of the life cycle; the
sporophyte is retained on the gametophyte and
dependent throughout out its life-cycle for survival
2) Lack Vasculature - Attribute of all other land plants in
the sporophyte phase that transports nutrients and
water and aids in rigidity
BRYOPHYTES - Representative Moss Life Cycle
Zygote
sporophyte
gametophyte
antheridium archegonium
spores
BRYOPHYTES - Characteristics unique from other land
plants
1) Gametophyte Dominant- The predominant vegetative
form is the gametophyte phase of the life cycle; the
sporophyte is retained on the gametophyte and
dependent throughout out its life-cycle for survival
2) Lack True Vasculature - Attribute of all other land
plants in the sporophyte phase that transports
nutrients and water and aids in rigidity
LIVERWORTS (Marchantiophyta)
LAND PLANT PHYLOGENY
-Liverworts
(From Simpson 2006)
LIVERWORTS
Elater: functions in spore dispersal; elongate, spiral-
walled haploid cells that are hygroscopic (change
shape and move in response to moisture content)
Elater
Spores
Capsule
(sporangium)Elaters
LIVERWORTS
Oil Bodies: membrane bound organelles containing oil
found in the cells of most liverworts, function is not
known.
Figure 1. Diagram of relationships of major clades as resolved from
parsimony and Bayesian analyses of 5 loci (including chloroplast, nuclear, and
mitochondrial DNA). Numbers above the branches are Maximum Parsimony
bootstrap values/homogeneous Bayesian posterior probabilities (PPs)/5-
partition Bayesian PPs/14-partition Bayesian PPs. The Bryologist (Forrest et
al., 2006)
LIVERWORTS
Phylogenetic hypothesis - Based on molecular data
Leafy
Thalloid
LIVERWORTS5,500 - 9,000 species
-Gametophyte dominant
The vegetative body is thalloid, consisting of a thallus,
a flattened mass of tissue
- only a few cell layers thick, water uptake through
osmosis
-ventral (lower surface) has rhizoids, unicellular
elongate filaments that aid in anchorage and
absorption for external moisture retention and
multicellular scales
-the upper surface has air pores for gas exchange
or leafy, having two rows of lateral leaves and
frequently a third ventral row of reduced size along
a stem. Leaves are very thin (generally 1 cell layer)
and absorbent. Also have rhizoids.
Gametophyte: Thalloid
Form
Rhizoids
Thallus
Thallus
LIVERWORTS
-Gametophyte dominant
The vegetative body is thalloid, consisting of a thallus,
a flattened mass of tissue
- only a few cell layers thick, water uptake through
osmosis
-ventral (lower surface) has rhizoids, unicellular
elongate filaments that aid in anchorage and
absorption for external moisture retention and
multicellular scales
-the upper surface has air pores for gas exchange.
or leafy, having two rows of lateral leaves and
frequently a third ventral row of reduced size along
a stem. Leaves are very thin (generally 1 cell layer)
and absorbent. Also have rhizoids.
Thallus upper surface: air pores for gas exchange
Air pore
LIVERWORTS
-Gametophyte dominant
The vegetative body is thalloid, consisting of a thallus,
a flattened mass of tissue
- only a few cell layers thick, water uptake through
osmosis
-ventral (lower surface) has rhizoids, unicellular
elongate filaments that aid in anchorage and
absorption for external moisture retention and
multicellular scales
-the upper surface has air pores for gas exchange.
or leafy, having two rows of lateral leaves and
frequently a third ventral row of reduced size along
a stem. Leaves are very thin (generally 1 cell layer)
and absorbent. Also have rhizoids.
Gametophyte: Leafy Form
-Not homologous with leaves of mosses, evolved
independently
Homology- Similarity that is due to common ancestryLateral leaves
Ventral leaf
LIVERWORTS
Special Features
1) Vegetative reproduction - gemmae and gemmae
cups
2) Gametangium- antheridium and archaegonium
(sometime retained on antheridiophores and
archegoniophores)
GAMETOPHYTE MITOTIC
(VEGETATIVE)
REPRODUCTION
Example: Gemmae Cups and
Gemmae from Thalloid
Liverworts
Gemmae
Gemmae
Gemmae cup
Gemmae cup
Gametophyte - Archegonium holds egg; Antheridium holds
sperm.
-Sperm attracted to egg via excreted proteins
-Some Liverworts have specialized structures that retain
archegonia (Archegoniophore) and antheridia
(Antheridiophore).
antheridiophore
antheridiophore
antheridium
archegoniophore
archegonium
Marchantia
archegoniophore
Gametophyte - archegonium holds egg; antheridium holds
sperm. Example: Leafy liverwort (Porella).
antheridium archegonium
LIVERWORTS
-Sporophyte - retained on gametophyte
• Sporangium - matures before seta (1N stalk)
• Spores - dispersed simultaneously from explosive
capsule with elaters.
• Homosporous: All spores identical in size.
Capsule 2N
Seta
Gametophyte
Sporophyte Phase: Capsule contains the sporangium
Immature
sporophyt
e
surrounde
d by
calyptra
elaters
Capsule with
apical sutures
Capsule wall
Sporophyte Phase: Capsule contains the sporangium
which produce spores through meiosis. Spores are
dispersed when capsule splits and spiraled elaters dry.
Review:
Liverwort Life Cycle
√
2N 2N
2N
Liverwort - life cycle
HORNWORTS (ANTHOCEROTOPHYTA)