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Vascular Plants without Seeds (Megaphyll line of evolution (origin…
Vascular Plants without Seeds
Microphyll line of evolution
may have come from zosterophyllophtyes
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morphology
true roots allowed them to grow to tremendous size
microphylls=enations in division Lycophyta
heterospory
cones and strobili
clustered together in sporgangia
protection
microspores/megaspores germinated to become microgametophytes/megagametophytes
=necessary precondition for the evolution of seeds
extant genera
Lycopodium
all small herbs w/ prostrate rhizomes, true roots & short, upright branches
microphylls= spirally arranged on their stems; no secondary growth
Selaginellas
ligule
on upper surface of leaves
Isoetes
AKA quillhorts
also have ligules
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similar to Stylites
grow in wet, muddy areas
Lycophytes
Concepts
monobiontic life cycle
only one multicellular generation
interpopulation hypothesis
dibiontic life cycle
multicellular gametophyte and sporophyte
transformation theory
Megaphyll line of evolution
Trimerophytes
trend of overtopping
pseudomonopodial branching
sinlge main trunk
extinct
origin
megaphylls=leaves that evolved from branch stems
evolution summarized by telome theory
telome=of last dichotomy
planation=all subdivisions of a lateral branch become aligned in one plane
webbing=parenchyma develops between telomes and lower branches
sporohyll= sporangium-bearing leaf-like structure
megaphylls AKA euphyllophytes
monilophytes
euphyllophyte sister clade
ferns and fern allies
equisetophytes
horsetails/scouring rushes included
all living plants are herbs w/o secondary growth
usually less than 1mm tall
have sporangiophore (umbrella shaped)
Ferns
can occur in almost any habitat
sporophyte
leaf trace at node of
leaf gap
leaves
may be leathery or delicate
sori on underside; where meiosis occurs
two types of sporangia
eusporangium= initiated when several surface cells divide
leptosporangium=initiated when single surface cell divides
Early vascular plants
rhyniophytes
equal dichotomous branching
homosporous
types of xylem organization
endarch protostele= protoxylem at center & metaxylem differentiates at edge
exarch protostele= metaxylem at center & protoxylem at edges
siphonpstele=pith at center; in stems of ferns and seed plants
zosterophyllophtyes
small herbs w/o secondary growth
lateral sporangia that open transversely; xylem is exarch protostele
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enations
thin scales to increase surface area for photosynthesis
Vascular cryptograms
ferns and fern allies
have vascular tissue
reproduction is hidden bc they lack seeds
plants of this chapter
