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Chapter 21: Vascular Plants Without Seeds (The Megaphyll Line of Evolution…
Chapter 21: Vascular Plants Without Seeds
The Microphyll Line of Evolution: Lycophytes
Morphology
microphyll
“almost” leaf
evolution from small enations
evolution of true roots
growth, absorption, anchor
vascular cambium flaw
cells troubled by radial longitudinal division
Heterospory
extinct lycophytes
sporangia clustered
cones or
strobili
protect
homosporous
heterosporous
megaspores
megagametophytes
microspores
microgametophytes
necessary for seed evolution
Extant Genera
Selaginellas
small flap of tissue
ligule
heterosporous
lycopodium
microphylls
no secondary growth
heterotrphic
isoetes
heterosporous
sporangia extensively
additional cortex parenchyma
CAM
no stomata
convergent evolution
endosporial development
The Megaphyll Line of Evolution: Euphyllophytes
Trimerophytes
overtopping
pseudomonopodial branching
Origin of Megaphylls (Euphylls)
leaves on gametophytes of nonvascular plants
enations / microphylls of zosterophyllophytes and lycophytes
megaphylls
leaves that evolved from branch systems
euphyllophytes
telome
theory
megaphyll evolution
planation
webbing
Monilophytes
#
united by synamorphies
roots have exarch xylem
have megaphylls
have 30 kilo base inversion of plastic DNA
Equisetophytes
horsetails / scouring rushes
no secondary growth
Ferns
Eusporangia & Leptosporangia
eusporangium
surface cells undergo divisions
multilayered plate of cells
leptosporangia
Psilotum & Tmesipteris
leaf trace
diverges from siphonostele
leave small segment of vascular cylinder as paranchyma
leaf gap
leptosporangiate ferns
most popular and known
Early Vascular Plants
Rhyniophytes
Xylem Structure of Early Vascular Plants
no pith
xylem mass -
protostele
endarch
protoxylem located in center
metaxylem on outer edge
siphonostele
evolved later
seed plants & ferns
pith present
sporangia
terminal
open along the side
Zosterophyllophytes
no secondary growth
sporangia
lateral
opened transversely (across top)
small herbs
protoxylem - exarch
metaxylem in center
xylem mass and protoxylem on edges as groups next to phloem
enations
- outgrowths
increased photosynthetic surface area
#
The Term “Vascular Cryptograms”
ferns & fern allies
vascular tissue & lack seeds
symplesiomorphies
synapomorphies
shared derived features
shared ancestral features
life cycle
dibiontic
multicellular gametophyte & sporophyte
monobiontic
one multicellular generation
transformation theory
dibontic life cycle
diverted into two clades
vascular plants
nonvascular plants
interpolation hypothesis
#
sporophyte had to exist
by zygote dividing mitotically
related
connect to sporangia
connect to microphylls
resembled zosterophyllophytes sporangia
megaphyls
sister clade
