Please enable JavaScript.
Coggle requires JavaScript to display documents.
Vascular Plants W/O Seeds (The Megaphyll Line of Evolution (Origin of…
Vascular Plants W/O Seeds
Concepts
monobiontic
only one multicellular generation
A zygote undergoes only meiosis
Producing more spores
Grow into new gametophores
Zygote cannot undergo mitosis
Cannot produce a sporophyte
thus evolution into a dibiontic
interpolation hypothesis
small sporophyte came into existence
When a zygote germinated mitotically
instead of meiotically
Sporophyte generation would gradually evolve
dibiontic life cycle
#
all known fossil plants have one
Each species has a multicellular gametophyte
Also a multicellular sporophyte
Alternation of generations
transformation theory
after the dibiontic life cycle originated
both gametophytes and sporophytes
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 are equal size and vigor
Had an epidermis with cuticle
a cortex of parenchyma
simple bundle of xylem
composed of tracheas
With annular secondary walls
Ends of branches were swollen
Contained large/multicellular masses
of sporogenous tissue
surrounded by several layers of sterile cells
only central cells were sporogenous
sporangium had to open to release spores
Rhyniophytes
Cooksonia
homosporous
no separate microspores
no separate megaspores
Fossils that have these are <-
Ex)
Rhynia
and
Aglaophyton
Prostrate rhizome
upright naked stems
Terminal sporangia
Xylem Structure of Early Vascular Plants
two types of xylem organization
Endarch protostele
protoxylem is located in the center
narrow
Small
Metaxylem differentiates on the outer edge
changes after expanded a few days
longer time=larger expansion
Exarch protostele
metaxylem located in the center
protoxylem located along outer edges
Several groups next to phloem
Protostele
solid mass of xylem in center
NO PITH
Siphonostele
Did not evolve until much later
Pith is present
located in center
occurs in stems of ferns and seed plants
Xylem is often preserved in fossils
Zosterophyllophytes
named after principal genus
Zosterophyllum
Small herbs without secondary growth
similar to rhyniophytes
3 characters that are different
sporangia opened transversely on top edge
Sporangia are lateral
not terminal
xylem was an exarch protostele
protoxylem on outer edge
metaxylem in the center
Grow as small bunches
approx. 15cm high
upper stem had a cuticle
ordinary epidermal cells
stomata
lower stem did not have those things
Enations
outgrowths on the surface
ranged from small to long/thin
Increased photosynthetic surface area
The term "Vascular Cryptogams"
"ferns and fern allies"
have vascular tissue
they lack seeds
reproduction is hidden(crypto)
Share ancestral features
with symplesiomorphies
Do not indicate they are closely related
The Microphyll Line of Evolution
#
Extant Genera
Lycopodium
also known as "ground pine" or "club moss"
fairly common from tropical to arctic forests
Spirally arranged on their stems
Secondary growth never occurs
may be arranged in cones or along shoots
All are homosporous
spores germinate
grow into bisexual gametophytes
produce both antheridia and archegonia
selaginella
less common in temperate NA
plants are smaller
easily overlooked
mistaken to be mosses
Ex)
S.lepidophylla
Curls up
Turns brown
Appears dead upon drying
uncurls
regrets when moistened
Morphology
Lycophytes are known as microphylls
"Micro-" refers to small enations
some may be 78cm long
Lycophytes have true roots
allow them to anchor firmly to roots
absorb efficiently
Able to grow to large sizes
Lycophytes have
Lateral sporangia
Exarch protosteles
Ancestor from Zosterophyllum
Heterospory
Clustered together in compass groups
Cones
Clumped together
Strobili
Singular
Protect the plant
Convergent evolution characteristics
Leaves
Roots
Secondary Growth
Almost Seeds
The Megaphyll Line of Evolution
Monilophytes
3 types of synapomorphies
have megaphylls
have 30-kilobase inversion
large single copy region
of their plastid DNA
Roots have exarch xylem
Euphyllophytes
2 sister clades
Monilophytes
known as ferns
the woody plants
Equisetophytes
Horsetails
Consists of several genera of extinct plants
and one genus
Equisetum
with 15 extant species
All living plants are herbs
without secondary growth
usually less than 1m tall
Monopodial Growth
Main trunk
Lateral branches
True roots
True leaves
Sporangiphore
umbrella-shaped
short stalk
flat, shield-shaped head
sporangia project
parallel to the sporangiophore stalk
Origin of Megaphylls
3 types of homoplasic
enations/microphylls of zosterophyllophytes
Megaphylls
Leaves of gametophytes on non-v plants
Megaphylls
leaves that evolved from branch systems
present in all seed plants
ferns
equisetophytes
Telome Theory
Megaphyll evolution is summarized by
Telomes
Ultimate twigs
those of the last dichotomy
Consists of
main stem
smooth, cylindrical
Dichotomously branching lateral stems
Sporophyll
branch system produced sporangia
sporangium-bearing leaf like structure
Outcompeted those of microphylls
Euphyllophytes
all megaphyllous plants
form a monophyletic cycle
Ferns
Leptosporangiate Ferns
Greater number of species of ferns
Approx. 12,000
Ferns can be found in almost any habitat
All ferns are perennial and herbaceous
Leaf Trace
#
Diverges from the siphonostele
Leaving a small segment
of vascular cylinder
as only parenchyma
Leaf Gap
Region of only parenchyma
Sori
Clusters of sporangia
Where meiosis occurs
Singular form is Sorus
Trimerophytes
Overtoping
Trimerophytes had an unequal branching
One stem was more vigorous
In later species
inequality was so pronounced
main stems/lateral stems were easily identifiable
Pseudomonopodial branching
Single main trunk
Rather than a series of dichotomies
Plants have small lateral branches
Some fertile
bearing sporangia
other stiles, act as leaves
Both are homosporous
Dibiontic are vascular
Leaf trace and Xylem both have a siphonostele
