Review ideas about what it takes for a plant to live on land instead of in water.
UV protection (pigments-
e.g anthocyanin)
protect embryo from desiccation inside a special structure
roots
leaves
vascular system
cuticle
stomata
mycorrhiza e.g truffle
learn more about what plants need to live on land here and here.
Because of ability to protect embryo, the land plants are sometimes called the "embryophytes"
Classification and Evolution of the land plants.
See chapter 22 - 24 of Berg text.
General images of all the groups described below, along with some views of their important structural features can be found at:
http://botit.botany.wisc.edu:16080/images/130/
General info on plant evolution here.
Land plants can be divided into vascular and non-vascular plants.
Vascular plants sometimes collectively called tracheophytes.
Plant vascular system consists, essentially, of tubes used to carry water.
Non-vascular plants include three important phyla with certain characteristics in common:
No vascular tissue.
No root system.
Motile sperm require water... hence these organisms are like the amphibians of the plant world.
Bryophte sperm have 2 flagella placed at the sperm head. Animal and fungi sperm flagella are placed at the sperm tail end.
Sperm swim toward the egg and fertilize it. Sperm find egg using chemosensory apparatus (smell).
Often separate sexes for gameteophyte.
Gameteophytes often have have male parts called antheridia and female parts called archegonia. These produce sperm and eggs respectively.
Members of these non-vascular plant phyla are generally small and most must live somewhere damp. Water is required for reproduction. However, many mosses practice a form of hibernation where they dry out in times of drought and come back to life after rainfall.
Bryophytes have only limited ability to carry water around their tissues or stand upright.
Alternation of generations is evident, gameteophyte is dominant.
(Sporophyte is
diploid generation and produces spores. Gameteophyte is haploid and produces
gametes (= sex cells = pollen and eggs in flowering plants, sperm and eggs in
most others).
As plants evolved from bryophytes to angiosperms we tend to see a transition
from dominant gameteophyte to dominant sporophyte.)
In non-vascular plants, the sporophyte is small, always attached to the gameteophyte. Sporophyte is completely dependant on the gametophyte for nutrition.
Spores are released from the the sporophyte and these turn into a new haploid gametophyte.
"Old Man's Cave", Ohio is an excellent place to see many members of this group.
Three bryophyte phyla:
1) Hornworts (phylum Anthocerophyta)
Image of a hornwort here.
This image shows a plate-like gameteophyte with upright sporophytes growing out of it.
Notice that the hornworts look quite similar to the green algae Coleochaete.
Presence of stomata a little puzzling. Stomata are present on both the gametophyte and sporophyte. These stomata do not open and close like higher plant stomata.
Nostoc (Nitrogen fixing cyanobacteria) colonies live inside hornwort gametophytes. Nostoc enters the gametophyte via the open stomata.
Another common name is "moonwort" in some areas.
2) Liverworts (phylum Hepatophyta) (Hepaticophyta?)
Image of liverwort here.
Come in leafy and thalloid forms.
Image shows thalloid genus Marchantia gameteophyte.
Reproduction can be sexual, (involving the production of sperm and eggs on attached, umbrella-like antheridia and archegonia) or asexual through the vegatative production and dispersal of "gemmae", which grow into new clones of the parent.
Liverworts are the only bryophyte with membrane bound oil bodies in every cell. These oils may have medicinal value, and liverworts are sometimes used in traditional herbal medicines.
Riccia can live both on land and floating on water. The shape of the plant changes depends where it lives.
Liverworts never have stomata, but they do have air chambers in their gametophytes which can open and close.
3) Moss (phylum Bryophyta)
Image of a moss here.
Note the bushy gameteophyte at the bottom with sporophyte consisting of a seta and a capsule growing upwards.
Spores are released from the capsule and grow into new male or female gameteophyte. In some species the spores germinate to produce a simple microscopic filament called a protonema, which gradually matures into the gameteophyte.
The “leaves” of moss are not true leaves and are only one cell layer thick.
Sphagnum is the only economically important moss. Gardeners use sphagnum to retain moisture in soil (sphagnum has very thick cell walls which absorb water).
Specific types of moss can be used to identity minerals in the soil. The Copper moss grows on soil enriched with copper. Leucobryum (white pillow moss) grows on soils enriched with calcium.
Mosses are divided into 2 large groups- those with gametophytes that grow upwards and don’t branch and those with gametophytes that spread over soil and do branch.
Some species may grow underwater (Java moss - Vesicularia). Java moss is a common ornamental species in freshwater aquaria.
Dr. Fred Sack of
OSU uses moss to study how plants respond to gravity. His team works with the
protonema of the moss Ceratodon. They use the protonema form because
it grows easily on small agar plates and is easy to observe under a microscope.
Dr Sack and his team of graduate students have flown moss on 2 NASA space shuttles.
He flew moss on the space shuttle Columbia, which tragically broke up during
entry to the atmosphere. Fred’s moss was found in Texas and he was the
only biological researcher to collect data from the Columbia mission.
For more on this story see here
and here.
Vascular plants can be divided into seed plants and seedless plants.
Seedless vascular plants include four living phyla:
1) Club mosses and other lycophytes (Phylum Lycophyta)
Some groups of
lycophytes have underground gametophytes that require mycorhizzae to live. These
gametophytes can live for many years.
Lycopodium spores contain votatile oils. These spores are used as flash
powder in old fashioned photography.
200 - 400 million years ago, Lycophytes formed huge forests - important source of decomposing plant material that was compressed and aged under layers of sediment until it turned into coal.
Today lycophytes are smaller and much less common.
Lycophyte rhizomes (root-like structures) observed in first lab by preparing coal ball peels.
2) Ferns (Phylum Pterophyta) (Pteridophyta?)
Ferns produce brownish spore-releasing structures on the underside of their leaves called SORI. "The underside of a fern is a sight for sore eyes" (soris.... geddit ??).
Oh never mind.
Fern gameteophytes will be observed in lab.
Ferns once formed huge trees.
Some aquatic forms, eg Azolla which is important as a fertilizer in rice paddies - contains nitrogen fixing cyanobacteria.
Know the terms used to describe fern parts, which are NOT the same as the language used to name flowering plant parts.
3) Whisk ferns (Phylum Psilotophyta)
(images) (more info...) (more more info..)
Pteridophytes are
probably just ferns, based on sperm morphology and many molecular studies.
The text books haven’t kept up with the research.
Extremely common in greenhouses. Look for Psilotum
growing as a weed in many different pots in the OSU greenhouse (ask the staff
if you cannot find it).
Gametophytes are very similar to Lycopod gametophytes; they look like little
sub-terranian turds.
4) Horsetails (Phylum Sphenophyta)
(images) (more info...) (more more info...)
Sometimes called "scouring rush", used by pioneers to clean pots and pans because it contains silica (glass).
Don't you think that the giant horsetail looks a bit like Chara?
There are also several extinct phyla of seedless vascular plants, but we won't worry about them.
General features of seedles vascular plants:
Sporophyte dominant.
Range of different reproductive strategies and structures.
Alternation of generations usually visible.
Sporophyte dominant but gametophyte is quite well developed.
Sperm still has to swim from antheridia to archegonia of gameteophyte.
Sperm have many flagella.
Sporophyte grows from fertilized embryo within the gameteophyte.
