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Chapter 21: Vascular Plants Without Seeds (The Term "Vascular…
Chapter 21: Vascular Plants Without Seeds
The Microphyll Line of Evolution: Lycophytes
Morphology
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Similiar to zosterophyllophytes
Difference: Entations were large
Up to 4 cm
contained well developed vascular tissue
Increased photosynthesis
Microphylls: evolution from small enations
evolution of true roots
allowed anchor and absorption which allowed tremendous size
Wood resembled that of pines and other conifers
Heterospory
sporangia clustered together in cones or strobili
has microspores and megaspores
necessary for evolution of seeds
some megaspore retained within the sporophyll protected
convergent evolution, seeds, roots, secondary growth and almost seeds
Extant Genera
Lycopodium
All living species are small herbs
Homosporous
Selaginella
heterosporous
ligule on surface of leaves
Ancient
Inside megaspore wall, megagametophytes develop
Isoetes
quillworts
grow muddy places
Heterosporous
Early Vascular Plants
Rhyniophytes
earliest fossils that were vascular land plants
equal dichotomous branching: both branches being of equal size and vigor
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homosporous: no seperate microspores and megaspores
only central cells were sporogenous
Xylem Structure of Early Vascular Plants
Protostele: solid mass of xylem with no pith
Endarch protostele: protoxylem in center w/ metaxylem @ outer edges
Protoxylem: xylem that differentiates where cells are small and thin
metaxylem: Differentiates after cells expanded
Exarch Protostele: Metaxyle at center protoxylem at exges
Siphonostele: pith is present
Ferns and seed plants
Zosterophyllophytes
Small herbs without secondary growth
Grew in small bunches
upper portions of stems had cuticcle
Sporangia lateral, not terminal
Sporangia opened transversely along top
Xylem was an exarch protostele
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The Term "Vascular Cryptogams"
Vascular Cryptograms/ferns and fern allies
vas. tissue
hidden reproduction
ancestor features: symplesiomorphies
not indicated that their closely related
Lack seeds, flowers, fruits
Shared features: synapomorphies
Not grouped together formally
evolutionary advancement based
Term Bryophyte: often used for all nonvascular plants
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Indicates they're not all related
The Megaphyll Line of Evolution: Euphyllophytes
Monilophytes
Euphyllophytes: megaphyllous plants
megaphylls
30 kilobase inversion
roots have exxarch xylem
Two sister clades
Monilophytes: ferns and cern allies
Lignophytes: woody plants
Lignophytes:woody plants
Origin of Megaphylls (Euphylls)
megaphylls: leaves evolved from branch system present in all
telome theory:telomes, planation, webbiing, sporophyll, euphyllophytes
planation: all subdivisions become aligned on one plane
telomes: ultimate twigs/last of dichotomy
webbing: parenchyma that develops between telomes
sporophyll: branch system that produces sporangia
Ferns
Psilotum and Tmesipteris
The two simplest of living vascular plants
Psiotum: Whisk ferns
highly derived&simplified ferns
prostrate rhizomes and upright stems
Branch dichotomously
No pith
Tmersipteris
Limited to Australasia and other South Pacific Islands
Eusporangia and Leptosporangia
eusporangium:
Leptosporangia:
Leptosporangiate ferns: ferns that are familiar
leaf trace: diverges from siphonostele leaving small segment of vas cylinder as parenchyma
Leaf gap: vascular cylinder of parenchya
Sori (sorus singular): clusters of sporangia where meiosis occurs
Trimerophytes
Overtopping: Unequal branching one stem was more vigorous
Pseudomonopodial Branching: single main trunk
Genera of Extinct Plants
Trimerophyton
Overtopping
Psilophyton
Pertica
Pseudomonopodial branching
Concepts
interpolation hypothesis
zygote germinated mitotically
Not meiosis
sporophyte evolved while gametophyte evolution stayed small
Monobiontic
only one muticellular generation
zygote only does meiosis
produce spores to grow into gametophytes
transformation theory
after dibiontic life cycle
both gametophyte and sporophyte enlarged
alternation of ismorphic generations
All extant plants have dibiontic life cycle
muticellular gametophyte and sporophyte
