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Chapter 21: Vascular Plants Without Seeds (The Megaphyll Line:…
Chapter 21: Vascular Plants Without Seeds
Early Vascular Plants
Zosterophyllophytes
small herbs lacking secondary growth
lateral sporangia
sporangia opened transversely
branched dichotomously
homosporous
enations
Rhyniophytes
Equal dicotomous branching
epidermis with cuticle
lack of leaves
simple bundle of xylem
sporangia at end of branches
homosporous
Xylem structure
protostele
endarch
photoxylem in center
metaxylem differentiates on outer edge
exarch
metaxylem in center
protoxylem on outer edge
siphonostele
pith present in center
evolved later
The Microphyll Line: Lycophytes
Morphology
large enations
microphylls
evolution of true roots
Heterospory
sporangia clustered
cones
strobili
represent ancient line of evolution
leaves
roots
secondary growth
Extant Genera
Lycopodium
true roots
short, upright branches
Microphylls spirally arranged on stem
sporangia arranged in cones or along shoots
homosporous
Selaginella
heterosporous
microgametes develop in spore
ligule
Isoetes
small corn like stem
roots attached below
leaves above
heterosporous
The Megaphyll Line: Euphyllopytes
Trimerophytes
overtopping
psuedomonopodial branching
unequal branching
Origin of Megaphylls
Telome theory
megaphylls
planation
webbing
sporophyll
euphyllophytes
Equisetophytes
monopodial growth
trunk
lateral branches
true leaves and roots
vascular cambium evolved independently
ferns
leptosporangiate
habitat is shady forest
sporophyte
single axis
true roots
megaphyllus leaves
homosporous
Eusporangia
surface cells undergo periclinal divisions
outer cells develop into the sporgania wall
inner proliferate into sponge tissue
Monilophytes
synapomorphies
roots have exarch xylem
megaphylls
30-kilobased inversion in plastid DNA
Leptosporangia
single surface cell divides periclinally
forms small outward protrusion
Vascular Cryptogams
ferns and fern allies
vascular tissues
reproduction is "hidden"
lacking features
seeds
flowers
fruits
