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Vascular Plants Without Seeds (The Megaphyll Line of Evolution:…
Vascular Plants Without Seeds
Concepts of Vascular Plants Without Seeds
Dibiontic life cycle
Species have a multi-cellular gametophyte and also a multi-cellular sporophyte.
monobiontic
having only one multi-cellular generation.
interpolation hypothesis
states that when a small sporophyte came into existence when a zygote germinated mitotically instead of meiotically
transformation theory
states- postulates that after the dibiontic life cycle originated,both gametophyte and sporophyte became larger, more complex, and vascularized, in a life cycle with an alternation of isomorphic generations
Early Vascular Plants
Rhyniophytes
equal dichotomous branching
both branches being of equal size and vigor
rhyniophytes
common name for Rhynia and its relatives, the earliest vascular plants.
Xylem Structure of Early Vascular Plants
Prostele
Solid mass of xylem with no pith in the center in early vascular plants
endarch prostele
protoxylem is located in the center and metaxylem differentiates on the outer edge of the xylem mass
exarch protostele
metaxylem located in the center of the xylem mass and protoxylem on the edges as several groups next to the phloem
siphonostele
pith is present in the center, as ouccrs in stems of ferns and seed plants
seed plants
plants that bear seeds as part of its reproductive cycle
Zosterophyllophytes
Zosterophyllophytes
small herbs without secondary growth
enations
outgrowths that ranged from quite small to long, thin scales
The Microphyll Line of Evolution: Lycophytes
Morphology
microphylls
type of leaf that evolved from an enation
Heterospory
cones or strobili
clusters of sporangia in compact groups for protection
Extant Genera
ligule
small flap of tissue on the upper surface of Selaginella leaves
The Megaphyll Line of Evolution: Euphyllophytes
Trimerophytes
overtopping
unequal branching in which one stem was more vigorous
pseudomonopodial branching
a single main trunk rather than a series of dichotomies
Origin of Megaphylls (Euphylls)
megaphylls
leaves that evolved from branch systems and are present in all seed plants, ferns, and equisetophytes
telome theory
the theory that leaves of arthrophytes, ferns, and seed plants evolved from branch systems by overtopping, planation, and webbing
telomes
the ultimate twigs, those of the last dichotomy
Planation
all branching occurred in one plane, resulting in a flat system
webbing
concept that the lamina originated by the production of parenchyma cells between the telomes
sporophyll
a sporangium-bearing, leaf like structure
euphyllophytes
all megaphyllous plants form a monophyletic clade
Monilophytes
monilophytes
the clade containing ferns in a broad sense
lignophytes
synonym for a plant that develops wood
Equisetophytes
horsetails or scouring rushes
several genre of extinct plants and one genus, Equisetum, with 15 extant species
sporangiophore
a stalked, umbrella like structure that bears sporangia
Monopodial growth
a main trunk, lateral branches, true leaves, and true roots
Ferns
Leptosporangiate ferns
ferns that we are familiar with
leaf trace
a vascular bundle that extends from the stem vascular bundles through the cortex and enters a leaf
leaf gap
diverges from the siphonostele, leaving a small segment of the vascular cylinder as just parenchyma
Sori
clusters of sporangia where meiosis occurs
Eusporangia and Leptosporangia
eusporangium
serveral surface cells undergo periclinal divisions resulting in a small multilayered plate of cells
Leptosporangia
initiated when a single surface cell divides periclinally and forms a small outward protrusion
The Term "Vascular Cryptogam"
vascular cryptogams
have vascular tissue and lack seeds their reproduction is hidden
