Mosses and ferns
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Mosses and Ferns. Evolutionary developments necessary for plants to colonize land. Stage One: Becoming multicellular. Occurred in water. Enables specialized tissues to develop. Stage Two: Developing sporangia. Enables dispersal on land. Stage Three: Developing a large sporophyte.

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Mosses and Ferns

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Mosses and ferns

Mosses and Ferns


Evolutionary developments necessary for plants to colonize land

Evolutionary developments necessary for plants to colonize land

Stage One: Becoming multicellular

Occurred in water

Enables specialized tissues to develop

Stage Two: Developing sporangia

Enables dispersal on land

Stage Three: Developing a large sporophyte

Confers competitive advantage

Provides perennial spore production

Stage Four: Removing dependence of fertilization on a film of water

Enables survival in dry environments


History of evolution of major plant types on land

History of evolution of major plant types on land


Stage one of adaptation to living on land

Stage One of adaptation to living on land

Land plants required several adaptations to be successful that require multi-cellular tissues:

The land that plants colonized was hostile to life.

Soil development was minimal.

mechanical strength for support,

exposed light catching surfaces,

anchoring system,

conducting system for water,

system for obtaining mineral nutrients,

a way to restrict water loss in desiccating air,

a means of reproducing and dispersing on land


Mosses and ferns

Devonian plant community found at Rhynie, in Scotland. A reed-like marsh, 370-380 million years ago.

Asteroxylon

MAIN FEATURES

Simple dichotomous branching

Sporangia

!5 to 30 cm tall

No roots

Stomata with guard cells

Most had a central vascular strand

Cuticle

Asteroxylon had leaves –without a vascular connection

Devonian plant community


Mosses and ferns

Plants living in water release spores and gametes that swim and may be helped to dispersed by water movement

Dispersal was solved first – through production of sporangia.

The important feature of sporangia is that they lift spores above the ground so they can be dispersed by the wind

To live on land plants faced two challenges for their reproduction:

1.Dispersal

2. Fertilization

angeion is Latin for case

So a sporangia is asporecase


Mosses and ferns

Meiosis in the sporangium producing haploid spores.

Retention of the zygote by the female gametophyte

Delayed meiosis and growth of the sporophyte by mitosis

1.Dispersal

Developing

sporophyte

Zygote

Gametophyte

Archegonium

Stage Two: Developing sporangia

Mosses


Mosses and ferns

Eight Terms to Learn to understand

Alternation of Generations of Land Plants

Spores– haploid, single cells produced by meiosis

The word “phyte” is Greek for plant

Gametes– collective term for sperm and egg

Gametophyte– haploid plant that develops from a spore and produces gametes by mitosis

Gametangium– a “case” holding gametes

Archegonium– flask–shaped container holding the egg cell.(Ancientgonad) The female gametangium.

Antheridium– The male gametangium

Sporophyte– diploid plant that grows from the zygote and produces spores by meiosis

Sporangium– the “case” holding spores


Moss life cycle

Moss life cycle

Fig. 25.4, p. 406

Mature sporophyte (spore-producing structure and stalk), still dependent on gametophyte.

zygote

rhizoid

Zygote grows, develops into a sporophyte while still attached to gametophyte.

Diploid Stage

Meiosis

Fertiliztion

Haploid Stage

Spores form by way of meiosis and are released.

Sperm reach eggs by moving through rain drops or film of water on the plant surface.

Spores germinate. Some grow and develop into male gametophytes.

sperm-producing structure at shoot tip of male gametophyte.

egg-producing structure at shoot tip of female gametophyte.

Other germinating spores grow and develop into female gametophytes.


Moss sporophyte

Moss sporophyte

Top of capsule


Developing protonema

Developing protonema


Moss antheridium and archegonium

Moss antheridium and archegonium


Important life cycle features of mosses

Important life cycle features of mosses

Mitosis

Spores

n

Gametes (?)

HAPLOID

Meiosis

Fusion (syngamy)

DIPLOID

Zygote

2n

Mitosis

Development of gametophyte thallus

Female gamete remains attached to the haploid thallus

Development of sporophyte thallus – remains attached to gametophyte


Dessication tolerance in tortula ruralis

Dessication tolerance in Tortula ruralis

RAPID WATER LOSS

Constitutive Cellular

Protection

Induction of

Recovery and Repair

Mechanisms

Hydrated

Dry

Rehydrated

Hormone ?


Spagnum the bog forming species

Spagnum – the bog-forming species

The species forms clumps- minimizing surface area to volume ratio.

Unique leaf cells (hyaline cells) of Spahgnum species enable the plant to absorb up to 20 times its own dry weight of water.

Fig. 25.5, p. 407


How can we characterize mosses

How can we characterize mosses?


Mosses and ferns

Large size enables competition as well as effective spore dispersal. The perennial root stock enables continued frond and spore production from year to year

Sporophyte originally grows from a gametophyte and then develops roots, rhizome, and fronds

Fronds growing from a rhizome

Ferns

Stage Three: Developing a large sporophyte

In ferns the sporophyte is only dependent on the gametophyte for obtaining nutrient, water, and physical support when it is first formed.


Fern life cycle

Fern life cycle

The sporophyte (still attached to the gametophyte) grows, develops.

sorus (one of the spore-producing structures)

zygote

Diploid Stage

fertilization

meiosis

Haploid Stage

egg-producing structure

Spores develop.

Spores are released

mature gametophyte (underside)

Archegonia

egg

sperm-producing structure

Spore germinates, grows into a gametophyte.

sperm

Antheridia


Sporangia

Sporangia

http://departments.bloomu.edu/biology/chamuris/concepts2/labimg.html

Polypodium spp

sori

sporangia

A sorus


Magnified sporangia

Magnified sporangia

Polypodium spp

Sporangia

Developing spores


Gametophyte

Polypodium spp

Gametophyte

Developing sporophyte

Gametophyte


Arrangement of sporangia on two ferns

Arrangement of sporangia on two ferns

In lines on a broadleaved type

At the end of the leaves

Adiantum

Asplenium


Tree ferns

Tree ferns

Cibotium menziesiiin habitat in Hawaii.  Photo courtesy of Peter Richardson.

Cyathea australis with the uncurling croziers visible.  Photo courtesy of Scott Ridges

Conducting tissue


How can we characterize ferns

How can we characterize ferns?


Coal formation

Coal formation

Jungle-like forests of the Carboniferous were dominated by giant ancestors of club mosses, horsetails, ferns, conifers, and cycads.

Most of the plant fossils found in the coals and associated sedimentary rocks show no annual growth rings, suggesting rapid growth rates and lack of seasonal variation in the climate (tropical).

Anaerobic conditions and periodic inundations of the sea


Early carboniferous

Early Carboniferous

Equator

Appalachians

Britain

Ice cap


Mosses and ferns

Equator

Appalachians

Britain

Ice cap


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