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Vascular Plants Without Seeds (Early Vascular Plants (Zosterophylelophytes…
Vascular Plants Without Seeds
Concepts:
Dibiontic life cycle
each species has a multicellular gametophyte and also multicellular sporophyte
Monobiontic
one multicellular generation
zygote undergoes only meiosis, producing more spores that will grow into new gametophyte
Interpolation hypothesis
small sporophyte came into existence when a zygote germinated mitotically instead of meiotically
Transformation theory
after the dibiontic life cycle originated, both gametophyte and sporophyte become larger, complex, vascularized, ln life cycle.
Early Vascular Plants
Equal dichotomous branching
both branches being of equal size and vigor
Rhyniophytes
fossils that have general characters
endarch protostele
protoxylem is located in center and metaxylem differentiates on outer edge of xylem mass
Protostele
center is a solid mass of xylem with no pith
exarch protostele
other type of stele present in early vascular plants
metaxylem located in center of xylem mass and protoxylem on the edges as several groups next to phloem
Siphonostele
stele that evolved later
one in which pith is present in center as occurs in the stems of ferns
Zosterophylelophytes
group of early vascular plants
named after the principal genus Zosterophyllum
small herbs without secondary growth
Enations
outgrowths
range from quite small to large, thin scales
The Microphyll Line of Evolution: Lycophytes
Morphology
enations large (up to 4cm)
Contained single well-developed trace of vascular tissue
Microphylls
enations in the division Lycophyta
Heterospory
cones (strobili)
in extinct and extant lycophytes sporangia are clustered together in compact groups
protection
Extant Genera
Lycopodium (ground pine or club moss)
fairly common in forest
small with prostrate rhizomes
have true roots and short upright branches
Ligule
small flap of tissue
found on selaginellas
The Megaphyll Line of Evolution: Euphyllophytes
Trimerophytes
overtopping
unequal branching I which one stem was more vigorous.
Pseudomonopodial branching
single main trunk rather than a series of dichotomies
Origin of Megaphylls (Euphylls)
Megaphylls
leaves that evolve from branch systems and are present in all seed plants, ferns, and equisetophytes
Telomes
ultimate twigs of the last dichotomy
Planation
all subdivisions of lateral branch become aligned in one planeand parenchyma develop between telomes
Webbing
Even lower branches
Sporophyll
if branching system involved in this evolution produced sporangia
resulting structure would not be just a leaf but a sporophyll
Euphyllophytes
We believe all megaphyllous plants form a monophyletic clade now reffered to as a euphyllophytes
Monilophytes
current studies suggest that megaphyllous plants united by three synapomorphies:
have megaphylls
have 30-kilobase inversion in the large singlcopy region of their plastid DNA
roots have exarch xylem
Contain two sister clades
monilophytes
aka ferns
lignophytes
aka woody plants
Equisetophytes
has 15 extant species
known as horsetails or scouring rushes
Sporangiophore
reproductive structures in groups of 5-10 located on umbrella shaped object.
monopodial growth
main trunk, lateral branches, true leaves, and true roots
leptosporangiate ferns
monilophytes have more than 12000 species almost all are leptosporangiate ferns
ferns that are familiar to you
Leaf trace
at each node
diverges from the siphonostele
Leaf Gap
small segment of the vascular cylinder as just parenchyma
Sori
underside of the leaf
eusporangium
initiated when several surface cells undergo periclinal divisions
resulting in small multilayered plate of cells
Leptosporangia
initiated when a single surface cell divides periclinally and forms small outward protrusion
The term "Vascular Cryptogams"
plants in this chapter have been referred to informally as vascular cryptogams
or often as ferns and fern allies
name indicates they have vascular tissue and that their reproduction is hidden
