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Vascular Plants Without Seeds (megaphyll line of evolution: euphyllophytes…
Vascular Plants Without Seeds
early vascular plants
rhyniophytes
simple upright stems, short cylinders w/o leaves
equal dichotomous branching
both branches being of equal size & vigor
epidermis w/ cuticle, cortex of parenchyma, & simple bundle of xylem composed of tracheids w/ annular secondary walls
central cells were sporogenous, sporangium had to open to release the spores
no separate microspore & megaspores
xylem structure
protostele
center is a solid mass of xylem w/o a pith
endarch protostele
protoxylem is located in the center & metaxylem differentiates on the outer edge of the xylem mass
exarch protostele
with metaxylem located in the center of the xylem mass & protoxylem on the edges as several groups next to the phloem
later evolved
siphonostele
pith is present in center
zosterophyllophytes
small herbs w/o secondary growth
3 distant characteristics
sporangia were lateral
sporangia opened transversely along the top edge
xylem was exarch protostele
enations
outward growths
increased photosynthetic surface area of plants
microphyll line of evolution: lycophytes
lycophytes have lateral sporangia & exarch protosteles
large enations 4cm
microphylls
large enations of lycophyta
cone/stroblil
clustered sporangia in compact groups used as protection
some species became heterosporous
ligule
small flap of tissue on the upper surface of selaginella
megaphyll line of evolution: euphyllophytes
overtopping
unequal branching in which one stem was more vigorous
pseudomonopodial branching
a single main trunk rather than a series of dichotomies
3 distinct types of homoplasic
(1) leaves on gametophytes of nonvascular plants
(2) enations/microphylls of zosterophyllophytes & lycophytes
(3)
megaphylls
leaves that evolved from branch systems & are present in all seed plants , ferns, & equisetophytes
evolution is summarized by
telome theory
telomes
ultimate twigs (those of the last dichotomy)
planation
all subdivisions of a lateral branch aligned in one plane
webbing
parenchyma develops btwn telomes & even lower branches
sporophyll
production of sporangia would result in a sporangium-bearing, leaf like structure
euphyllophyte
monophyletic clade
equisetophytes
all herbs w/o secondary growth, usually <1 m tall
ex: horsetails/scouring rushes
monopodial growth
main trunk, lateral branches, true leaves, & true roots
ferns
leptosporangiate ferns
what most people are familiar with
at each node a
leaf trace
diverges from siphonostele
leaf gap
a small segment of vascular cylinder as just parenchyma left behind from leaf trace
sori
located on the underside of the leaf; clusters of sporangia where meiosis occurs
eusporangia & leptosporangia
eusporangium
initiated when several cells undergo periclinal divisions, resulting in small multi. layered plate cells
leptosporangia
initiated when a single surface cell divides periclinally & forms a small outward protrusion
vascular cryptogams
features these plants lack: seeds, fruit, flowers, etc
referring to a grade, basically a level of evolutionary advancement
