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Chapter 21: Vascular Plants Without Seeds - Coggle Diagram
Chapter 21: Vascular Plants Without Seeds
Early Vascular Plants
Rhyniophytes
earliest fossil of vascular land plants:
Cooksonia
extinct plant genus
Rhynia
&
Aglaophyton
similar to
Cooksonia
Lyonophyto
&
Sciadophyton
gametophytes
stem ends flattened cup-shape, contain gametangia (antheridia & archegonia)
never contain sporangia
Xylem Structure of Early Vascular Plants
2 Types of Xylem organization
both, center is solid mass of xylem w/ no pith
endarch
protostele: protoxylem located @ center & metaxylem differentiates on outer edge of mass
#equisetophyte stem endarch
#fern stem endarch
exarch
protostele: metaxylem @ center, protoxylem on edges
developed later:
siphonostele,
pith present in center
(called
protostele
)
Zosterophyllophytes
small herbs without secondary growth
grew in small bunches approx. 15cm high
similar to rhyniophytes
3 differences
sporangia lateral, not terminal
sporangia open transversely along top edge
xylem exarch protostele
upper portions of stems had cuticle, epidermal cells, stomata
lower portion of stems did not
some had outgrowths called
enations
, ranged from small to long thin scales
The Microphyll Line of Evolution:
Lycophytes
#resemble zosterophyllophytes
distinct line of evolution out of early land plants, resembling zosterophyllophytes
Morphology
enations large, up to 4cm long
contained single well-developed trace of vasc. tissue
called
microphylls
in Lycophyta
Heterospory
many lycophytes sporangia clustered in
cones
or
strobili
necessary precondition for the evolution of seeds
Lepidostrobus
&
Lepidophloios
megaspores developed into megagametophytes (w/o enlarging)
Extant Genera
Lycopodium:
common in forests from tropical to arctic
all living species (approx. 200) small herbs
all
homosporous
microphylls spirally arranged on stems
secondary growth never occurs
Selaginella:
less common in temperate N. America
heterosporous, megagametophyte develops in megaspore wall
megaspore not retained on sporophyte, not seed-like
distinguished from lycopodiums by small flap of tissue,
ligule
, on upper surface of its leaves
Isoetes:
grow in wet, muddy areas that occasionally dry
often called
quillworts
small, corn-like stem
roots attached below, leaves attached above
hetersporous, almost every leaf contains sporangia
The Megaphyll Line of Evolution:
Euphyllophytes
Trimerophytes
includes genera
Trimerophyton
,
Psilophyton
, and
Pertica
Pertica
displays
pseudomonipodial branching
(single main trunk)
overtopping:
unequal branching in which one stem is more vigorous
Origin of Megaphylls (Euphylls)
3 distinct types of homoplasic structures called leaves
leaves on gametophytes of nonvascular plants
enations/microphylls of zosterophyllophytes & lycophytes
#enations came from zosterophyllophytes
megaphylls, evolved from branch systems
present in all seed plants/ferns/equisetophytes
evolution summarized by
telome theory
subdivisions of lateral branch become aligned in one plane
parenchyma develops between telomes & lower branches
all megaphyllous plants form monophyletic clade called
euphyllophytes
Monilophytes
megaphyllous plants united by
3
synapomorphies
roots have
exarch
xylem
have
megaphylls
have a
30-kilobase inversion
in large single-copy region of plastid DNA
many monilophytes known as ferns
Equisetophytes
living plants all herbs without secondary growth, usually less than 1m tall
true roots present
stem has pith, protoxylem forms next to pith
endarch siphonostele
sporangia always occur in groups of 5 to 10
located on umbrella-shaped
sporangiophore
homosporous
Ferns
early ferns appear in Devonian Period
most familiar fern:
leptosporangiate
can be found in almost any habitat, though forests/lakesides typical
all perennial & herbaceous
none woody, but can reach size of small tree
sporophyte consists of single axis (vertical shoot or horizontal rhizome)
bears both true roots & megaphyllous leaves
vasc. system of stem is
endarch siphonostele
at nodes
leaf trace
diverges from siphonostele, leaves small section as just parenchyma
leaves can be leathery/delicate/thick/thin
underside of leaf are
sori
, clusters of sporangia where meiosis occurs
leaf primordia have distinct apical cell
known as
leaf gap
have 2 types of sporangia
eusporangium
initiated when surface cells undergo periclinal division
outer cells develop into sporangium wall, inner into sporogenous tissue
leptosporangia
initiated when single surface cell divides periclinally & forms small protrusion
after several more divisions it results in small set of sporogenous cells & thin sterile cell covering
Term “Vascular
Cryptograms
”
aka ferns & fern allies
have vascular tissue and lack seeds so reprod. is “hidden”
lack seeds, flowers, fruits, etc.
when term used its referring to level of evolution