Seedless Vascular Plants Flashcards
Why are Bryophytes limited in their ability to radiate and adapt to novel environments?
- lack of cuticle
- Lack of a developed conduction tissue (xylem and phloem)
What was hypothesized to have eventually pushed the evolution of vascular tissue allowing the plant to be lifted off the ground?
Selection pressures
Leading to:
- greater access to sunlight
- more successful spore dispersal
Vascular tissue lead to the development of organs such as….
- Roots (water absorption)
- Leaves (photosynthesis)
- Stems (structural support)
Lignin
the tough, decay-resistant compound that composes wood
- allows for much greater structural support which allowed plants to grow significantly taller
Diploidy
- offers more opportunity for diversification
- gave way for greater development of the plant body for the expression of more alleles
Branching Sporophytes
- offered more sites in which meiosis could take place
- increased opportunities for variation
- more options in an increasingly competitive environment
Tracheophytes
Plants with vascular tissue
Increased physical and nutritional support afforded by the vascular tissue allows for….
- larger physical size of the plant
- increased range as there is less dependence on free water
- better adaption to terrestrial habitats
- new methods of spore dispersal now open to the plant due to greater height and range
With vascular tissue there is no development of…
cambial tissue
Without vascular tissue there’s increasing independence of…
the sporophyte from the gametophyte
autotrophic sporophyte
In Seedless Vascular Plants…..
- The sporophyte is now the dominant phase of the life cycle (a-o-g between diploid and a haploid sporophyte)
- Leaves possess developed cuticle
- Gamete transfer and fertilization is still carried out by water
- The spores germinate to form an avascular gametophyte or prothallus (monoecious/dioecious) which is independent from the sporophyte and is usually much smaller
Pteridophytes (Vascular plants)
- Main plant body is a diploid sporophyte
- Cuticle is well developed
- True roots and leaves
- Vascular tissue
- Archegonia with short neck having 4 rows of cells vertically
- Sporophyte is differentiated into root, stem and leaves
- Sporophyte is initially dependent on gametophyte
- Sporophyte is AUTOTROPHIC at maturity
Ferns (Pteridophytes)
- Range from a few cm through 20 m tall (eg. Climbers, herbs, “tree” ferns)
- Most are herbaceous plants
- First major elaboration of leaf morphology:
a) Petiole and lamina differentiated (higher plants) with all possible variations on compound leaf theme
b) Sporophyte now the dominant form- larger than the gametophyte
Ferns’ Four Phyla
- Psilophyta
- Equisetophyta
- Lycopodiophyta:
a) Microsporophylls
b) Varied sporophyte forms
c) Some heterosporous - Polypodiophyta:
a) The true ferns
b) Large sporophyte
c) Some homosporous
Psilophyta
aka Whisk ferns
- small, green whisk-like plants
- associated with extinct group of plants called the psilophytes
- lack true leaves and roots
- include the oldest known land plants with vascular tissue
- Sporophyte has:
a) enations
b) creeping subterranean rhizome and a cylindrical branching stem with a central vascular strand (protostelic)
c) Rhizoids emerge along the rhizome
d) Classified with ferns due to similarities in the gametophyte generation
e) Homosporous
slide 12 for image
Enations
scale-like microsporophylls
Equisetophyta
Horsetails and scouring rushes
- Ribbed stems rough to feel (SiO2)
- Whorled enations
- Sporophyte has:
a) Aerial ventrical stems with nodes and internodes (protostelic) with canals
b) Stem develops from a subterranean
c) Numerous stomata
d) Rhizoids emerge along the rhizome - Classified with ferns due to similarities in the gametophyte generation
- Homosporous
slide 17 for image
Lycopodiophyta
-
Lycopodium sp.
(Club Moss) - Selaginella plana
Polypodiophyta
- Well developed sporophyte, eg. Nephrolepis sp., Azolla, Cyathea sp.
- True roots: adventitious
- Stems: subterranean rhizome
- Fronds
slides 22, 23 and 24 for images
Fronds
clusters of leaves or megaphylls
slide 21 for image
Sexual Reproduction
- Seedless vascular plants carry out their a-o-g in either a homosporous or heterosporous
- Homosporous:
a) this life cycle involves one size of spore
b) this spore produces a monoecious gametophyte which produces egg and sperm cells - Heterosporous:
a) this life cycle results in two sizes of spores, a megaspore (female) and a microspore (male)
b) these spores produce separate gametophytes, producing egg and sperm cells respectively
Reproduction-Sporangia
- Tapetal layer:
a) nourishes the developing spores
b) coats the spores, forming surface features (eg. ridges and spines) - Thick wall:
a) Annulus
b) Stomium/Lip cells
c) Sporangial stalk/sporangiophore - Dehiscence liberates spores with the help of wind
slides 30 and 31 for images
Taxonomical characters of spore include:
a) Shape
b) Size
c) Surface geometry
d) Wall layers
Types of Sporangia
- Leptosporangia
- Eusporangia
Leptosporangia
- Arise from divisions of a single superficial epidermal cell initial
- Sporangial wall made up of one cell layer
- These ferns are more common
Eusporangia
- Arise from divisions of many epidermal cell initials
- Sporangial wall made up more than one cell layer
- Hold many more spores
Reproduction-Gametophyte
- Diminuitive surficial thalloid Gametophyte or prothallus:
a) Usually less than 1 cm
b) Variously shaped
c) Most often photosynthetic
d) Monoecious or dioecious
e) Gamete transfer requires water for the flagellate antherozoids/sperm cells
f) Self-sterility operative
(slides 38, 39 and 41 for images)
