The Vascular Seedless Plants

1
The Vascular Seedless Plants Some General
Characteristics
Xylem elements containing lignin transport
water dissolved nutrients, and also provide
support phloëm transports synthesized foods
The sporophyte generation is dominant and long
lived, the gametophyte generation being smaller
but nutritionally independent Success on land
is aided by vascular system, cuticle and stomata
2
Generalized Life Cycle of Seedless Vascular
Plants, showing Sporic Meiosis
n.b. similarity to bryophyte life-cycle
3
Other Similarities to Bryophytes
Eggs are produced in archegonia and motile
sperms in antheridia A film of moisture is
required for fertilization to occur The
pigments are Chlorophyll a and b and
carotenoids Cell walls are of cellulose and
the carbohydrate stored is starch
4
Classification of Vascular Seedless Plants
Division PSILOTOPHYTA - Whisk Ferns Division
LYCOPODOPHYTA- Club Mosses Division
EQUISETOPHYTA - Horsetails Division
PTERIDOPHYTA - Ferns
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Division PSILOTOPHYTA - Whisk Ferns
Psilotum nudum, the Whisk Fern, is found in
subtropical regions of the southeastern United
States and Asia
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Dichotomous aerial branches bearing sporangia
Psilotum nudum - the Whisk Fern
Sporangia are fused in threes (synangia)
subtended by paired bracts
Synangia
Aerial shoot with scale leaves
Dehisced synangium
Three-angled branch with scale leaves
Rhizome with rhizoids
7
Photomicrographs of aerial stems of Psilotum in
cross-section
Stoma--
Phloëm
Xylem
Cortex
Epidermis
Protoxylem
Phloëm
Metaxylem
This type of fluted xylem cylinder, which appears
star-shaped in cross-section, is known as an
ACTINOSTELE. Note that the protoxylem is exarch.
Closeup of stele
8
Types of Stele
Ectophloic siphonostele
Haplostele
Actinostele
Plectostele
Atactostele
Amphiphloic siphonostele
Dictyostele
Eustele
Haplosteles, actinosteles and plectosteles are
types of protosteles
9
Psilotum nudum -an older stem and a rhizome in
cross-section
Symbiotic fungi
Phloëm
Pith
A B are cross-sections of an aerial stem (note
actinostele) and C is that of a rhizome (note
haplostele)
In B, note that there is an outer
chlorenchymatous cortex (for photosynthesis), a
sclerenchymatous middle cortex (for support), and
a parenchymatous inner cortex (for storage).
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Psilotum nudum - synangia
Plant with mature, yellow sporangia
Synangium seen in cross-section of fertile stem
Synangium dehiscing to release spores
11
Psilotum - gametophyte morphology and
anatomy
Antheridium
Rhizoid
Archegonium
Prothallus
The occasional occurrence of tracheids, phloëm
and endodermis in Psilotum gametophytes
supports the homologous theory of alternation of
generations
Drawing of a fertile Psilotum gametophyte.
Gametophytes are subterranean.
12
Maturation of Psilotum archegonium prior to
fertilization
13
Psilotum - Maturing Antheridium
Immature antherozoïds (sperms)
Mature antherozoïds
Longitudinal section of antheridium
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Life History of Psilotum
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Tmesipteris
T. parva epiphytic on trunk of tree fern in
Australia
T.lanceolata in New Caledonia
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Primitive Vascular Plants of the Devonian period
(408-387 years b.p.)
From left to centre are Cooksonia Rhynia
(Rhyniophyta) and Zosterophyllum
(Zosterophyllophyta). On the right, back to
front, are Psilophyton (Trimerophytophyta),
Drepanophycus and Protolepidodendron
(Microphyllophyta)
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Division RHYNIOPHYTA
Cooksonia
Horneophyton
Rhynia
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Stelar Differences between Rhyniophytes and
Zosterophyllophytes
Rhynia, with endarch protoxylem
Zosterophyllum, with exarch protoxylem
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Relationships between the Psilotophyta and the
Rhyniophyta
Although members of the current Psilotophyta
and the fossil Rhyniophyta appear to be very
similar, it is now believed that the
Psilotophytes are secondarily primitive