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Ch. 21 Vascular plants without seeds (The Microphyll line of evolution:…
Ch. 21 Vascular plants without seeds
Dibiontic life cycle
all extant plants
All known fossil plants
each species has a multicellular gametophyte and sporophyte
monobiontic Life cycle
includes some algae
has only one multicellular generation
zygote cannot undergo mitosis and form a sporophyte
embryophytes
from monbiontic to dibiontic
interpolation hypothesis
a small sporophyte came into existence when a zygote germinated mitotically instead of meiotically
the sporophyte generation would then gradually evolve to become more complex
transformation theory
sporophyte generation became more complex after the dibiontic life cycle originated
Early vascular plants
Rhyniophytes
homosporous
no separate micro and megaspores
equal dichotomous branching
both branches are equal size and vigor
epidermis with a cuticle
cortex of parenchyma
multicellular masses of sporogenous tissue
at the ends of branches
surrounded by a layer of sterile cells
Cooksonia, Rhynia, Aglaophyton
Xylem structure
Endarch protostele
Protoxylem
located in the center
metaxylem
differentiates on the outer edge
protostele
solid mass of xylem with no pith
Exarch protostele
Metaxylem
located in the center
protoxylem
located along the edges
siphonostele
pith is present in the center
Zosterophyllophytes
small herbs
no secondary growth
lateral sporangia
sporangia open transversely along the top edge
xylem= exarch protostele
The Microphyll line of evolution: lycophytes
Morphology
Large enations
up to 4 cm long
probably increased photosynthesis
Microphylls
ambiguously called leaves
Single, well developed trace of vascular tissue
true roots
anchoring
more growth
absorbtion
extinct lycophytes
some exhibit secondary growth
Lateral sporangia
Exarch protostele
Heterospory
Cones, or strobili
clustered groups of sporangia
provides protection
having both micro and megaspores
is necessary for the evolution of seeds
evolved convergent characteristics with seed plants
leaves
roots
secondary growth
Extant Genera
Lycopodium
Approximately 200 living species
small herbs
Prostrate Rhizomes
Selanginella
less common
often mistaken as mosses
small size
Ligule
small flap of tissue
no known function
Isoetes
quillworts
The Megaphyll line of evolution: Euphyllophytes
Trimerophytes
similar to rhyniophytes, but have several important features
Overtopping
one stem is more vigorous
Pseudomonopodial branching
One single trunk instead of a series of Dichotomies
Origin of Megaphylls
Megaphylls
Leaves evolved from branch systems
present in all seed plants, ferns, and equisetophytes
telome theory
Telomes
the ultimate twigs
planation
all lateral branches become aligned in one plane
webbing
parenchyma develops between between telomes
Euphyllophytes are united by three synapomorphies
exarch xylem
have megaphylls
have an inversion of their plastid DNA
Monilophytes
ferns
fern allies
Equisetophytes
Horsetails or scouring rushes
herbs with no secondary growth
usually less than 1m tall
aerial stems have a jointed structure
Sporangiophore
sporangia in groups of 5-10
Monopodial growth
Ferns
Can be found in almost any habitat
small leaves
contain large amounts of vascular tissue
Sori
on the underside of the leaf
clusters of sporangia
meiosis occurs here
Provide both photosynthesis and as sporophytes
typically homosporous
two types of sporangia
eusporangium
Leptosporangia
The term vascular cryptograms
ferns and fern allies
have vascular tissue
Hidden reproduction
crypto
lack seeds
