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Vascular Plants w/out Seeds (The Megaphyll Line of Evolution:…
Vascular Plants w/out Seeds
Early Vascular Plants
Rhyniophytes
Cooksonia
Earliest fossils that were vascular land plants
Genus of extinct plants
These plants had a:
Cortex of parenchyma
Simple bundle of xylem composed of tracheids w/ annular secondary walls
Epidermis w/ a cuticle
Equal dichotomous branching
Both branches being of equal size and vigor
Rhynia & Aglaophyton
Other Rhyniophytes
Early vascular plants similar to Cooksonia
These plants have:
Upright naked stems
Terminal sporangia
Prostrate rhizome
Horneophyton
Had sporophytes w/ naked axes
Branched dichotomously
Up to 20 cm tall
Have:
Stomata
Terminal sporangia
Zosterophyllophytes
Early vascular plants
Named after the principal genus Zosterophyllum
Small herbs w/out secondary growth
Similar to those of rhyniophytes
All are extinct
Upper portions of stems had:
Ordinary epidermal cells
Stomata
Cuticle
The Microphyll Line of Evolution: Lycophytes
Heterospory
Extinct & extant lycophytes sporangia
Are clustered together in compact groups
Called cones or strobili
These clusters protect them
Lycophytes are remarkable because:
They represent ancient line of evolution
Distinct from seed plants but having convergent evolution
In several characteristics which include:
Leaves
Roots
Secondary growth
Almost seeds
Extant Genera
Lycopodium
"ground pine" or "club moss"
Fairly common in forests from tropical regions to the arctic
Selaginella
Less common in temperate North America
Plants are smaller & easily overlooked
Or mistaken to be moss
S. lepidophylla
Known as resurrection plant
Turns brown when dehydrated
Turns green again when rehydrated
Morphology
Earliest lycophytes were members of the genera
Drepanophycus
Baragwanathia
Important advance:
Evolution of true roots
Which allowed lycophyte sporophytes to:
Anchor firmly
Absorb efficiently
& grow to tremendous size
Represent distinct evolution out of early land plants
Which resemble zosterophyllophytes
These plants have:
Lateral sporgania
Exarch protosteles
The Megaphyll Line of Evolution: Euphyllophytes
Monilophytes
United by 3 synamorphies:
1) Roots have exarch xylem
2) Have megaphylls
3) Have a 30-kilobase inversion
In the single copy region of their plastid DNA
Has two sister clades
Equisetophytes
Classified as division Arthrophyta
Consist of several genera of extinct plants & one genus
The one genus has 15 extant species
Known as horsetails or scouring rushes
The living plants are all herbs w/out secondary growth
Origin of Megaphylls (Euphylls)
3 distinct types of homoplasic structures occur in leaves
2) Enations/microphylls of zosterophyllophytes & lycophytes
3) Megaphylls
Leaves that evolved from branch systems
& are present in all seed plants, ferns & equisetophytes
1) Leaves on gametophytes of nonvascular plants
Summarized by telome theory
Trimerophytes
Most important is overtoppin
These plants had unequal branching
Which means one stem was more vigorous
Considered a distinct advancement
Out of rhyniophytes because of several special features
Pertica
Displays pseudomonopodial branching
Single main trunk instead of series of dichotomies
Ferns
First appeared in the Devonian Period
Then diversified greatly
Can be found in almost any habitat
"Typical" habitat is:
Moist, shady forests & lakesides
Some are found in dry, hot climates
The Term "Vascular Cryptograms"
This term refers to:
"ferns and fern allies"
This name indicates
Vascular tissue & because they lack seeds
These plants lack many features:
Flowers
Fruits
Seeds
