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Vascular Plants Without Seeds (The magaphyll Line of Evolution:…
Vascular Plants Without Seeds
The Microphyll Line of Evolution: Lycophytes
Morphology
earliest lycophytes were drepanophycus and Baragwanathia
large enations, contained vascular tissue
enations could be called leaves
called microphylls for clarity
"micro" due to evolution from small enations
increased photosynthesis
evolution of true roots
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Heterospory
cones
located in sporangia
protect them
strobili
located in sporangia
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protect them
many species remained homosporous
some species became heterosporous
have microspores and megaspores
gave rise to microgametophytes and megagametophytes
megagametophyte existed in megaspore
megaspore retained in sporophyll
necessary for evolution of seeds
Extant Genera
lycopodium
"ground pine" or "club moss"
common in forests to tropical regions to artic
all species
small herbs
prostrate rhizomes
true roots and short upright branches
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sporangia
may be arranged in cones
may be distributed along the shoots
selaginella
less common in temperate north america
smaller and overlooked to be mosses
apomorphic condition of being heterosporous
megagametophyte develops inside the megaspore
megaspore mot retained on the sporophyte
distinguished from lycopodiums by a ligule
isoetes
genus of ~60 quillworts
grow in wet, muddy areas that sometimes become dry
heterosporous
almost every leaf contains sporangia
anatomy and morphology
indicate many instances of convergent evolution with seed plants
efficient, elaborate leaves
wood
bark
roots
epidermis
stomatal spores and guard cells
large amounts of silica
stems tough and rigid
internal structures
stems have pith
protoxylem forms next to pith
vessels are rare
stem elongation stretches and tears cells
forms canals
The Term "Vascular Cryptogams"
indicates vascular tissue
because they lack seeds their reproduction is hidden
Shared ancestral features
these do not indicate they are closely related
when using the term
we are referring to a grade
a level of evolutionary advancement
The magaphyll Line of Evolution: Euphyllophytes
Trimerophytes
proposed for three extinct genera
timerophyton, psilophyton, and pertica
trimerophytons
distinct advancement out of rhyniophytes
most important is trend of overtopping
existed throw lower to upper devonian period
evolved into ancestors of ferns and seed plants
positioning of branches became regular and controlled
Origin of Megaphylls
at least three distinct types of homoplastic structures
leaves on gametophytes of nonvascular plants
enations of zosterophyllophytes and lycophytes
megaphylls
leaves that evolved from branch stems
present in all seed plants, ferns, and equisetophytes
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Monilophytes
united by three synapomorphies
roots have exarch xylem
have megaphylls
have a 30-kilobase inversion
Equisetophytes
consist of several genera and one genus
Equisetum
stems have jointed structure
leaves are small
reproductive structures are specialized
homosporous
sporangia in groups of 5-10
sporangia located on sporangiophore
spores germinate
develop into small green gametophytes
15 extant species
horse tails and scouring rishes
living plants are all herbs
have no secondary herbs
Ferns
appeared in the Devonian period
more than 12,000 species
can be found in almost any habitat
sporophyte has a single axis
either a vertical shoot or horizontal rhizome
gametophytes have no chlorophyll
are instead heterotrophic
at each node
leaf trace diverges from siphonostele
makes small segment of the vascular cylinder
only parenchyma
vascular cambium occurs in Botrychium
Early Vascular Plants
Zosterophyllophytes
principal genus Zosterophyllum
all extinct
grew as small bunches
stems have cuticle cells
stomata
lower portions lacked parts
Rhyniophytes
earliest definite plant fossils
belong to Cooksonia
Extinct species
upright cylanders
equal dichotomous branching
no stems
Lynophyton, sciadophyton
gametophytes
flatted cup-shaped ends of stems
Horneophyton
sporophytes
had naked axes that branched out
had stomata
Xylem Structure of early vascular plants
Two types of xylem organization
both the center is a protostele
endarch protostele
protoxylem is located in the center
metaxylem differentiates
exarch protostele
metaxylem located in the center
protoxylem is located outside
siphonostele
evolved later
pith is located in the center
occurs in ferns and seed plants
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