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Vascular Plants without Seeds (The Megaphyll Line of Evolution:…
Vascular Plants without Seeds
Concepts
Dibiontic life cycle
Have multicellular gametophytes and sporophytes
All extant plants and all known fossil plants
Monobiontic
Have one multicellular generation
Some algae
Interpopulation hypothesis
Hypothesis that explains sporophyte generation
Sporophytes came from zygotes dividing
Mitotically rather than meiotically
Transformation theory
Gametophytes and sporophytes grew large and vascularized
Early Vascular Plants
Rhyniophytes
Equal dichotomous branching
Both branches are equal size and vigor
Fossils with these characteristics are rhyniophytes
Sporangenous central cells
Equal dichotomous branching
Homosporous
Xylem structure of early vascular plants
Protostele
Solid mass of xylem with no pith
Endarch protostele
Protoxylem in center, metaxylem on the outer edge
Exarch protostele
Metaxylem in center, protoxylem on the edges
Siphonostele
Pith is present
Occurs in ferns and seed plants
Zosterophyllophytes
Small herbs without secondary growth
Enations
Outgrowths which increased photostynthetic surface area
The Microphyll Line of Evolution: Lycophytes
Morphology
Microphylls
Enations of the division Lycophyta
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Heterospory
Cones
AKA strobili
Sporangia that protect enations
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Extant Genera
Ligule
Small flap of tissue only in selaginellas
The Megaphyll Line of Evolution: Euphyllophtes
Trimerophytes
Overtopping
Unequal branching where one stem is more vigorous
Pseudomonopodial branching
A single main trunk rather than several dichotomies
Origin of megaphylls (euphylls)
3 homoplasic leaf structure
Leaves on gameteophytes (nonvascular)
Enations/microphylls (zosterophyllophytes and lycophytes)
Megaphylls- leaves evolved from branch systems (seed plants)
Telome theory
Telomes- branched lateral stems
Branches align on one plane (planation)
Parenchyma develops between telomes and lower branches (webbing)
If branches produce sporangia, sporophyll would form
Megaphyllous plants form monphyletic clades (euphyllophytes)
Monilophytes
Euphyllophytes are united by three synapomorphies
Roots have exarch xylem
Have megaphylls
Have 30-kilobase inversion in their plastid DNA
Euphyllophytes have two sister clades (moilophytes)
And woody plants (lignophytes)
Equisetophytes
Horsetails/scouring rushes
Reproductive structures (sporangia) form on the sporangiophore
Monopodial growth
A main trunk, lateral branches, true leaves and roots
Ferns
Leptosporangiate ferns
Modern day ferns
Leaf trace
Leaves a vascular cylinder called a leaf gap
Sori (singular sorus)
Cluslters of sporangia where meiosis occurs
Eusporangium
When surface cells undergo periclinal divisions
Leptosporangia
A single surface cell divides periclinally
The Term "Vascular Cryptogams"
Vascular Cryptograms (ferns and fern allies)
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All plants discussed in the chapter
