Transcript CB098-008.25_Early_Tracheophytes

The Early Tracheophytes:
Ferns and Relatives
Tracheophytes (Early and Late)
- Tracheophytes are vascular plants that posses, lignified water
conducting tissue.
- Tracheophytes are the vascular plants.
- Prior to the evolution of tracheophytes, bryophytes were the
dominant form of plant life on earth. However, having an efficient
transport system enable the tracheophytes to outcompete
bryophytes in many circumstances.
- Unlike bryophytes, tracheophytes have a branched sporophyte that
is dominant in the life cycle.
- Tracheophyte Characteristics:
1) Xylem and Phloem for transport.
2) Lignified transport vessels to support the plant.
3) Roots to absorb water while also anchoring & supporting the plant.
4) Leaves that increase the photosynthetic surface.
5) Life cycle with a dominant sporophyte generation.
The Early Tracheophytes are the Seedless Plants (Ferns & Relatives).
The Late Tracheophytes are the Seed Plants which are the
Gymnosperms (those bearing cones and having naked seeds) and
Angiosperms (flowering plants that have covered seeds & fruit).
A Cladogram of the Early Tracheophytes.
Tracheophytes (The
Vascular Plants) evolved
from bryophytes.
Tracheophytes are
highly specialized for life
on land and now
dominate the landscape.
The Early Tracheophytes
(Rhyniophytes, Lycophytes,
Monilophytes) and Late
Tracheophytes (The Seed
Plants, which are
Gymnosperms and
Angiosperms) are all
Tracheophytes.
Extinct
The Early Tracheophytes (Seedless Plants)
- The early tracheophytes are seedless.
- They reproduce by spores.
- The majority of the early tracheophytes are homosporous.
However, heterospory does occur.
- The early tracheophytes are successful and have
sporophytes that are more tolerant of life on dry land than
those of bryophytes because water movement is controlled
by lignified vascular tissue, stomata and an extensive
cuticle.
- Water is still important for early tracheophyte gametophyte.
Water outside the plant is necessary for sperm movement
from antheridia (Sperm-bearing organ) to archegonia (eggbearing organ).
Therefore, moist habitats are necessary.
Division Lycophyta
The lycophytes have laterally attached sporangia
instead of terminally attached.
A club moss (Lycopodium obscurum),
alive today.
Lepidodendron, a dominant tree of the coal age forest.
A Diorama Reconstruction of a Coal Age Forest.
The lycophyte line reached its peak of diversity and ecological
importance in the Coal Age (Carboniferous Period). Today,
lycophytes represent a mere remnant of their Coal Age diversity.
(Read blue box on pages 408-409).
The following divisions make
up the Monilophytes:
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Division Psilophyta
Division Ophioglossophyta
Division Sphenophyta
Division Pterophyta
The Monilophytes are mostly herbaceous
(nonwoody) plants.
Division Psilophyta – the Whisk Ferns
Members of this division are
often epiphytes.
An Epiphyte is a plant that grows on another
plant, yet is not parasitic.
A whisk fern (Psilotum nudum).
Division
Ophioglossophyta
- the Ophioglossalean
Ferns
Adder’s Tongue Fern
(Ophioglossum sp.)
These small plants are
members of the spring flora in
temperate regions and also are
found in disturbed or open
tropical sites. A few are
epiphytes. Ophioglossum has
the greatest number of
chromosomes of any plant, 2n
being as high as 1,250 in some
species.
Division Sphenophyta – Horsetails
Only 1 genus is present (Equisetum). Stems have complex anatomy.
Horsetails
Division Pterophyta – True Ferns
The true ferns have a leptosporangium, (a distinct sporangium type).
Complex leaves are
varied.
Sexual reproduction is
usually
homosporous (one
type of spore, which
then develops into a
bisexual
gametophyte).
12,000 known species
5 Orders
True Fern
True Fern Structure
Know the parts of the frond
(fern leaf) rachis, pinna,
pinnules.
Fiddlehead - young tightly coiled
fern fronds (leaves).
Stems are
underground and
fronds (leaves) are
above ground.
Remember, rhizomes
are underground
stems.
Fern Reproduction
Sori (singular, sorus) - a
grouping of sporangia;
especially characteristic
of ferns.
An individual sorus
consists of an indusium,
sporangia (specifically
leptosporangia with
annulus).
The underside of a holly leaf, showing
many scattered sori.
A section of one sorus, showing the umbrella-like
indusium that shelters the sporangia.
Indusium - membranous growth of the epidermis of a
fern leaf that covers a sorus.
A leptosporangium and the role of the annulus in
spore dispersal.
A Leptosporangium is a distinct
sporangium type. It has a long
stalk and a single layer making up
the wall and it has an annulus that
aids in spore dispersal by flicking
spores out of the sporangium.
True Fern Life Cycle
a) Mature Frond
b) Sori form and result in
meiosis.
c) A haploid spore settles on the
moist ground, germinates
into gametophyte.
d) Archegonia, the structures
that produce eggs, and the
antheridia, which produce
sperm, both develop on the
underside of the
gametophyte.
e) & f) Flagellated sperm swim
form antheridia to
archegonia (Usually another
gametophyte).
g) Zygote is nourished by
gametophyte.
h) Embryo sporophyte develops.
i) Young sporophyte develops
that is rooted in the soil
itself and is independent of
the gametophyte.
True Fern Reproduction
- Sporophyte (2n) is larger than gametophyte (n).
- Some ferns can reproduce vegetatively
(asexual reproduction) in the sporophyte or
gametophyte bodies.
- The fern life cycle usually doesn't involve
animals.
- Read blue box on 422.
BIO 141 Botany with Laboratory
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