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Ch 21 Vascular Plants Without Seeds (The Megaphyll Line of Evolution:…
Ch 21 Vascular Plants Without Seeds
Early Vascular Plants
Rhyniophytes
cooksonia
earliest fossils that were vascular plants
equal dichotomous branching
both branches of equal size and vigor
rhyniophytes
earliest vascular plants
protostele
solid mass of xylem and no pith
endarch protostele
protoxylem is located in center
metaxylem differentiates on outer edge of xylem mass
exarch protostele
metaxylem located in center of xylem
protoxylem on edges of several groups next to phloem
siphonostele
later evolved, pith in center
Zosterophyllophytes
another group of early vascular plants
enations
small projecting flap of tissue
thought to have been the ancestor of leaves in lycophytes
The Microphyll Line of Evolution: Lycophytes
Morphology
microphylls
type of leaf that evolved from an enation
present in lycophytes
Heterospory
cones/strobili
sporangia clustered together in compact groups
Extant Genera
ligule
small flaps of tissue
The Megaphyll Line of Evolution: Euphyllophytes
Trimerophytes
overtopping
trimerophytes had unequal branching and one stem was more vigorous
pseudomonopodial branching
single main trunk rather than a series of dichotomies
Origin of Megaphylls (Euphylls)
homoplastic structures
leaves on gametophytes
enations of zosterophyllsophytes
megaphylls
leaves that evolved from branch systems
telome theory
theory that leaves evolved from branching systems by overtopping, planation, and webbing
telome
twigs, last of dichotomy
planation
occurs in one plane, resulting in flat system
webbing
concept that lamina originated by the production of parenchyma cells between the telomes
sporophyll
sporangium-bearing, leaf-like structure
euphyllophytes
megaphyllous plants form a monophyletic clade
Monilophytes
two sister clades
lignophytes
woody plants
Equisetophytes
sporangiophore
umbrella shape
monopodial growth
main trunk, lateral branches, true leaves, true roots
Ferns
leaf gap
area above leaf trace where there is no conducting tissue
leptosporangiate ferns
familiar to us
more than 12,000 species
leaf trace
vascular bundle that extends from the stem vascular bundles through the cortex and enters a leaf
sori
clusters of sporangia where meiosis occurs
eusporangium
initiated when surface cells undergo periclinal divisions
leptosporangia
initiated when a single surface cell divides periclinally
forms a small outward protrusion
The Term "Vascular Cryptograms"
vascular cryptograms
ferns and fern allies
indicates they have vascular tissue
lack seeds so reproduction is hidden
