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Chapter: 21 Vascular Plants Without Seeds (The Megaphyll Line of…
Chapter: 21
Vascular Plants Without Seeds
Early Vascular Plants
Rhyniophytes
characteristics
equal dichotomous branching
central cells were sporogenous
epidermis with a cuticle
cortex of parenchyma
simple bundle of xylem
fossils
example
Zosterophytes
named after genus
Zosterophyllum
small herbs without secondary growth
three distinct features
sporangia opened transversely along top edge
xylem was an exarch protostele
lateral sporangia
plants grew as small bunches
The Microphyll Line of Evolution: Lycophytes
heterospory
cones/strobili
compact groups
protect the species
necessary precondition for evolution of seeds
extant genera
approximately 200
small herbs
have prostrate rhizomes
true roots
short upright branches
morphology
earliest lycophytes were similar to zosterophyllophytes
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important differences
large enations
contain a single developed trace of vascular tissue
evolution of true roots
optimized lycophyte sporophytes
The Megaphyll Line of Evolution: Euphyllophytes
Monilophytes
two sister clades
examples
ferns
Marattiales
fern allies
Psilotales
Equisetophytes
division of Arthrophyta
consist of several genera of extinct plants
aerial stems
jointed structure
whorl of fused leaves at the nodes
specialized reproductive structures
monopodial growth
origin of megaphylls (euphylls)
distinct homoplasic structure
leaves evolved from branch systems
present in all seed plants, ferns, and equisetophytes
telome theory
summarizes megaphyll evolution
Trimerophytes
advancement out of ryniophytes
have unequal branching
controlled positioning of branches
Ferns
can be found in almost any habitat
sporophyte consist of a single axis
each node has a leaf trace
leaves can be leathery or delicate
underside of leaf is known as the sori
most are homosporous
The Term "Vascular Cryptograms"
refers to ferns and fern allies
they lack:
seeds
fruits
flowers
