Seedless Vascular Plants
Chapter 17
Seedless vascular plants
• The descendants of certain lineages of
seedless vascular plants, with names such
as whisk ferns, lycophytes, horsetails, and
ferns,
Seedless Vascular Plants
• differ from bryophytes in that the
sporophyte does not remain attached to
the gametophyte (is free-living) and
• has well-developed vascular tissues.
• It is the larger, longer lived phase of the
life cycle.
Organization of the Vascular plant
body
• The sporophytes of early vascular
plants were dichotomously branched
Club moss sporophyte
Shoot system
Vascular system
Young Club moss sporophyte
Tissue systems
• Dermal- outer portion
• Vascular- conductive tissues (xylem and
phloem)
• Ground- vascular embedded within ground
• Root, stem and leaf vary in these tissues
•
•
•
•
•
Vascular Tissue
Approximately 93% of plant species are vascular plants.
Vascular plants contain vascular tissue.
There are two kinds of vascular tissue:
Xylem conducts water and minerals up from the soil.
The cell walls of xylem cells help support the plant.
• Phloem conducts organic nutrients from one part of
the plant to another.
• True roots, stems, and leaves are found only in
vascular plants because these structures must
contain vascular tissue.
• The sporophyte of vascular plants is dominant.
Gametophytes
• Although the sporophytes of seedless
vascular plants can live on land, their
gametophytes cannot because they lack
vascular tissues and the male gametes
must have water to reach the eggs.
Seedless vascular plants typically live in
wet, humid places.
Tracheids elements
• Conducting cells of the xylem (water and
minerals)
• Have lignified wall thickening
Sieve elements
• In contrast sieve elements, the conducting
cells of the phloem have soft walls and
often collapse after they die
Vessel elements
• Principle water conducting cells in
angiosperm (flowering plants)
• VE evolved independently in several
groups of vascular plants- Convergent
evolution
Vascular tissue
Located in the vascular cylinders or Steles
of Roots and Stems
• Primary xylem
• Primary phloem
• In some Vascular plants Pith (ground
tissue)
Vascular tissue
Leaf precursors
Found in SVP
Several types of Steles- vascular cylinders that contain
vascular tissue (xylem, phloem and ground tissue)
Two distinct kinds of leaves (phylls)
• Microphylls- small leaves
contain single strand of
vascular tissue (Isoetes –
long leaves)
• Megaphylls- associated
with stems that have
either siphonosteles and
eusteles
• Branching veins
Reproductive Systems
• All vascular plants are oogamous- have
large nonmotile eggs and small sperm that
swim or are conveyed to the egg
• All VP have an alternation of
heteromorphic generations ( sporophyte is
larger and more complex than the
gametophyte)
Larger and more complex than the gametophyte
Free living
Generalized life cycle of a vascular plant
Oogamy
• Favored in plants
• Only one of the kinds of gamete must
navigate across a hostile environment
Homosporous Vs Heterosporous
• Homosporous produces one type of spore
• Heterosporous produces two types of
spores
• Early vascular plants are homosporous i.e.
(including horsetails) and some lycophytes
• Heterosporous found in some lycophytes
and in all seed plants (convergent
evolution)
Microspores and Megaspores
• Microspores- male gametophyte
• Megaspores- female gametophyte
• Endosporic development (develop within
spore wall) unlike the homosporous
development
Evolution of the vascular plant
• The gametophytes of VP have become
smaller and simpler
• Relatively large gametophytes of
Homosporous plants are independent of
the sporophyte for their nutrition
• In contrast the gametophyte of many
heterosporous VP and seed plants are
dependent on the sporophyte for their
nutrition
The Living Phyla of Seedless
Vascular Plants
• Phylum Lycopodiophyta
–
–
–
–
Club mosses
Lycopodium lagopus
Selaginella
Isoetes
• Phylum Pteridophyta
–
–
–
–
Ferns
Water ferns- orders Marsileales and Salviniales
Psilotales
Equisetales (horsetail)
Phylum Lycopodiophyta
• Lycophytes were once tree-sized but now
are represented by small club mosses on
the forest floor.
• The sporophyte has true roots, stems, and
small leaves containing the vascular
tissue.
• Strobili bear spores that germinate to form
small, free-living gametophytes.
Family Lycopodiaceae Club mosses
• Most familiar type in Lycopodiophyta phylum
homosporic
Lycopodium lagopus- have strobili
Huperzia lucidula- lack strobili
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Family Selaginellaceae
Selaginella lepidophylla - resurrection
plant
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Selaginella rupestris- rock
spikemoss
Selaginella kraussianacreeping plant
Selaginella willdenovii
Selaginella
is heterosporic
Family Isoetaceae- Quillworts
Last remnant of the fossil tree lycopods
Lepidodendron (also known as the "Scale tree")
because of their peculiar secondary growthdevelopment of both wood and bark,
a modified shoot system and an upright stance.
heterosporic
presence of ligules
May be aquatic
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Phylum Pteridophyta
Ferns (Pterophyta)
• Most ferns have a perennial underground stem
(called a rhizome).
• Roots and fronds arise from the rhizome.
• Young fronds are coiled "fiddleheads".
• Mature fronds are divided into leaflets.
• Spores form on the lower surface of some
fronds.
• Sori are clusters of sporangia that release
spores that develop into small heart-shaped
gametophytes.
Phylum Pterophyta
Order Filicales
Homosporic
Most familiar order
Order
Filicales
Life cycle of a fern (polypodium)
homosporic
• In most ferns, the stem is a horizontal,
underground structure called a rhizome.
The leaves grow above-ground (see the
photograph above).
• A sorus (pl. sori) is a cluster of
sporangia. Sori are located on the
underside of the leaves.
VIDEO - Fern sporangia discharge (X40) (4.13 MB)
Water Ferns- Order Marsileales
and Salviniales
Marsilea polycarpa
Salvinia natans
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Water ferns are heterosporic
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The equisetophytesEquisetum- horsetails
Damp areas
Streams
Along edge of
woods
Jointed stems and
rough texture
Small scalelike
leaves whorled at
nodes
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