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Chapter 21: Vascular Plants Without Seeds (The Megaphyll Line of Evolution…
Chapter 21: Vascular Plants Without Seeds
Concept
dibiontic life cycle
all extant plant
fossil plants
each species has multicellular gametophyte
multiceullular sporophyte
monobiontic
some algae
Coleochaete
only one multicellular generation
zygote undergoes only meiosis
zygote can't undergoes mitosis&can'y grow into sporophytes
produce more spores that grow into new gametophytes
interpolation hypothesis
small sporophyte came into existence when zygote germinated mitotically instead of meiotically
transformation theory
an alternative hypothesis
after the dibiontic life cycle originated
both gametophyte&sporophyte became larger
more complex
vascularized
in life cycle with alternation of isomorphic generations
The Term "Vascular Cryptogams"
vascular cryptogams
ferns and fern allies
have vascular tissue
lack seeds their reproduction is hidden(crypto)
Early Vascular Plants
Rhyniophytes
equal dichotomous branching
both branches being of equal size and vigor
earliest fossils that definitely were vascular land plants belong to Cooksonia
a genus of extinct plants
rhyniophytes
fossils have general characters
plant of Cooksonia were homosporous
&no separate microspores&megap[ores
Zosterophyllophytes
another group of early vascular plants
name after the principal genus Zosterophyllum
small herb without secondary growth
many similar to rhyniophytes
three characteristics make us think they were a distinct group
sporangia were lateral
not terminal
sporangia opened transversely along the top edge naked(smooth)
branched dichotomously
enations
ranged from quite small to long
thin scales
several zosterophyllophytes had smooth surface
The Megaphyll Line of Evolution: Euphyllophytes
Trimerophytes
overtopping
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Trimerophytes had unequal branching in which one stem was more vigorous
pseudomonopodial branching
Pertica displays
single main trunk rather than series of dichotomies
Origin of Megaphylls(Euphylls)
megaphylls
leaves that evolved from branch systems
present in all seed planys
ferns
equisetophytes
sporophyll
sporangium-bearing
leaf-like structure
euphyllophytes
megaphyllous plants from monophyletic clade
Monilophytes
euphyllophytes
three synapomorphies
roots have exarch xylem
have megaphylls
have 30-kilobase inversion in the large single-copy region of their plastid DNA
two sister clades
monilophytes
lignophytes
wood plants
Equisetophytes
horsetails/scouring rushes
several genera of extinct plants
one genus
Equisetum
with 15 extant species
sporangiophore
reproductive structures in Equisetum are specialized
sporangia always occur in group of five to ten located on an umbrella-shaped
monopodial growth
main trunk
lateral branches
true leaves
true roots
Ferns
leptosporangiate ferns
have 15 species of living plants
rest of he monilophytes have more 12000 species
leaf trace
diverges from the siphonostele
leaving a small segment of the vascular cylinder as just parenchyma
region is leaf gap
The Microphyll Line of Evolution: Lycophytes
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Morophology
microphylls
"leaf" is an ambiguous term
enations in the division Lycophyta
clarity the term
"lycophyll" has been suggested recently
Heterospory
cones/strobili
many extinct&extant lycophytes sporangia are clustered together in compact groups
singular
strobilus
Extant Genera
ligule
selaginellas can be distinguished from lycopodiums by a small flap of tissue
upper surface of Selaginela leaves
Lycopodium
"group pine"
"club moss"
