Download Chapter 21-Seedless Plants Major modern plant groups All groups

Chapter 21-Seedless Plants
Major modern plant groups
All groups of land-adapted plants have a common set of characteristics:
-plant bodies composed of tissues produced by an apical meristem
-spores with tough walls
-life history of alternation of generations
-all plants produce their spores in multicellular enclosures called sporangia
Traits that characterize the 5 modern plant groups
DNA, fossils, and other characteristics have been used to construct plant phylogenies.
Plant phylogeny indicates:
Land-adapted plants form a monophyletic group (plants originated from a common ancestor).
Charophycean algae (Streptophyta) are the modern protists most closely related to plants.
Bryophytes – The First Land Plants
Bryophyte is the name for a group of related organisms that included the ancestor of all other land plants.
Based on the appearance of fossil bryophytes, the transition to land took place over 475 million years ago.
Bryophytes are rather simple organisms, but they are found in a wide variety of habitats and are highly diverse, with
over 25,000 described species.
Bryophytes are very important in many ecosystems:
Bryophytes have a number of features that are similar to their charophyte ancestors, but they also possess several
features that are clearly important for life on dry land.
Bryophyte features shared with charophytes:
•
•
•
•
•
•
similar pigmentation
starch production in the plastid
cell walls primarily of cellulose (no lignin)
a photosynthetic gametophyte
similarly structured sperm
a need for free water for sexual reproduction
Chara
Mnium
Key innovations that first appeared in bryophytes.
1.Sporophyte evolution
Zygote is retained on the gametophyte.
The zygote divides by mitosis to produce a multicellular sporophyte s
till attached to the gametophyte.
The bryophytes are the first plants with embryos.
In bryophytes, the embryos are immature sporophytes that are embedded in the tissue of the multicellular
gametophyte.
This arrangement of the sporophyte growing from within the gametophyte provides protection and nourishment for the
sporophyte and allow for the production of many spores that can withstand desiccation.
2. Gametophyte evolution
Large and elaborate gametophyte generation, similar to many charophytes and not found in other land plants.
Multicellular structures surround the gametes. These structures are called gametangia.
Key innovations that first appeared in bryophytes.
Structure of a liverwort (early bryophyte)
3. Stomata and cuticle
Structure of an angiosperm leaf
Stoma, with guard cells
Stomata are structures that allow gas exchange but at the same time reduce water loss.
The waxy cuticle also helps prevent water loss.
Bryophytes comprise three distinct lineages of plants that do not have lignified vascular tissue.
Hornworts – Phylum Anthocerotophyta
Liverworts – Phylum Marchantiophyta
Mosses –
Phylum Bryophyta
Bryophytes comprise three distinct lineages of plants that do not have lignified vascular tissue.
Hornworts – Phylum Anthocerotophyta
•
Simple thalloid gametophyte.
•
Form symbioses with cyanobacteria which enter the thallus through pores.
•
Only land plants with this algal characteristic.
Detail of the hornwort sporophyte.
Basic hornwort form. Note the simple sporophyte.
Hornworts are sometimes epiphytic but can be found free-living on clay banks.
Liverworts – Phylum Marchantiophyta
Grow primarily in moist, shady areas.
Two different types:
Thalloid liverworts
Resemble hornworts, but the thallus is held to the soil surface by single-celled rhizoids.
Leafy liverworts
Look more like a moss, with distinct leaves and stem.
Liverworts – Phylum Marchantiophyta
The thalloid genus Marchantia
The thallus has minute pores that function much like stomata.
Marchantia reproduces the gametophyte generation asexually through the production of small vegetative
structures called gemmae, which are produced in gemmae cups.
Marchantia also reproduces sexually.
Male structures, called antheridiophores, resemble very small umbrellas.
Liverworts – Phylum Marchantiophyta
The thalloid genus Marchantia
Marchantia also reproduces sexually.
Female structures, called archegoniophores, resemble little palm trees.
After fertilization, the sporophytes develop under the archegoniophores.
Leafy liverworts
Leafy liverworts are similar in appearance to mosses, but the leaves of liverworts have two or three distinct rows,
instead of the spiral arrangement of leaves on most mosses.
The resulting flattened appearance is rather distinctive.
Porella
Leafy liverworts
The archegonia appear at the tips of short leafy branches.
Antheridia are produced in the axils of leaves.
The leafy liverwort sporophyte is very simple.
Mosses – Division Bryophyta
Dawsonia, found in Australia and New
Zealand, to 60 cm tall.
www.sbs.auckland.ac.nz/info/schools/nzplants
The common moss Polytrichum, hair-cap moss
http://www.perspective.com/nature/plantae
Sphagnum, the moss of bogs.
botit.botany.wisc.edu/images/130/Bryophytes/Bryophyta/
Mnium, sometimes called carpet moss
http://home.clara.net/adhale/bryos
Mosses. Vegetative Structure
The first vegetative stage of the gametophyte is the protonema.
This stage looks very much like a filamentous green alga.
The “stems” of mosses have specialized tissues:
They have an epidermal layer, often with a cuticle.
The inner cells are called the cortex.
A central strand of conductive tissue is present in some mosses.
Central Strand
Cell types present in some mosses include hydroids, which conduct
water upward.
Leptoids, which move sugar throughout the plant.
These simple conductive tissues are the early evolutionary
steps toward the complex vascular systems of other land plants.
Mosses. Vegetative Structure
The leaves of mosses are not leaves in the true sense of the word.
They do not have conductive tissues that are present in the leaves of
vascular plants.
Mosses – Life Cycle
The sporophyte grows to form an upright capsule and
seta.
Haploid spores are produced and released from the
capsule.
The spores germinate into haploid male and female
gametophytes
Flagellate sperm are released from the antheridium and
travel to the archegonium where fertilization occurs.
The moss that you most commonly see is a
combination of the leafy gametophyte and
the sporophyte that does not have leaves.
The capsule, the region of the sporophyte where the spores are produced, is often covered by the calyptra.
The capsule may also have an operculum.
These features differ greatly among the various families of mosses.
The calyptra is a
membraneous
covering that is
actually a remnant
of the archegonial
wall.
Operculum covered by a
calyptra. The operculum
eventually pops off to
become the opening for
spore dispersal.
Mosses- Peristome teeth
The capsule opening of many mosses has a particular structure called perostome teeth.
When the moss dries, the teeth outcurve, which pulls spores out and discharges them.
Longitudinal section through a moss capsule showing all the features.
Study outline for Chapter 21-Bryophytes
Name the five modern plant groups.
What are the common set of characteristics that all groups of land-adapted plants share?
Which algae are most closely related to land plants?
When did the transition from water to land occur?
Define bryophyte.
How are bryophytes important in ecosystems?
Name the features that bryophytes share with charophytes.
Name the key innovations that appeared in bryophytes during the transition from water to land.
Define sporophyte evolution.
Define gametophyte evolution.
Define archegonium.
Define antheridium.
What are the three distinct lineages of bryophytes that do not have lignified vascular tissue?
What is the phylum for hornworts?
What is the phylum for liverworts?
What is the phylum for moss?
What is the difference between a thalloid liverwort and a leafy liverwort?
Define leptoid.
Define hydroid.
Label the structures in the liverwort Marchantia.
gemmae (n)
gemmae cups (n)
antheridophore (n)
antheridia (n)
archegoniophore (n)
archegonia (n)
developing sporophyte (2n)
Study outline for Chapter 21-Bryophytes
Define operculum.
Define seta.
Define protenema.
Define peristomal teeth.
Define calyptra.
Define leptoid.
Define hydroid.
Label the terms from the moss life cycle.
sporophyte
gametophyte
capsule
seta
protonema
antheridium
archegonium
egg
sperm
zygote
spores
Bryophytes- Label the following: hornworts, thallose liverwort, leafy liverwort and moss. List 3 characteristics for each
picture.