Lab 6 - Gymnosperms

Report
Lab 6
Gymnosperms
Gymnosperms
• seed bearing plants – but “naked seeds”
• often borne on cones
• do not produce flowers - angiosperms
Gymnosperms
Angiosperms
-reduced male gametophyte
(development of pollen grains)
-internal fertilization
-reduced female gametophyte
(development of ovules)
-naked seeds
-advanced vascular tissue
comprised of tracheids
-woody
-perennial
-reduced male gametophyte
(development of pollen grains)
-internal fertilization
-reduced female gametophyte
(development of ovules & an embryo sac)
-seeds – borne in fruits
-development of flowers
-advanced vascular tissue with tracheids and
vessel elements
-herbaceous and woody
-annuals and perennials
Gymnosperms
– Phylum Ginkgophyta - ginkos
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only one species left – Ginkgo biloba
deciduous leaves - fanlike formation
tolerates air pollution well
trees bear fleshy seeds that smell rancid
– Phylum Coniferophyta – largest group
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“cone-bearing”
Cycas revoluta
600 species of conifers
many are large trees
most are evergreens – retain their leaves throughout the year
Ginko biloba
Welwitschia
mirabilis.
Ephedra.
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found in subtropical and tropical regions
often confused with young palms
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most are less than 2m tall
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~25% are considered endangered
take a very long time to grow
stout, cylindrical trunk that does not branch
leaves are pinnate (“feathers” on a bird) are grow directly
from the trunk
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Macrozamia = 18m tall
9 to 10 genera – ~300 species total
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stout trunk with compound leaves
Phylum
Cycadophyta
central leaf stalk with parallel “ribs” emerging from the sides
leaves grow from the top of the crown down
Sago palm
Cycas revoluta
– produce seed and pollen cones on separate plants =
dioeicious
– pollen cones are spirally arranged microsporophylls
that bear clusters of microsporangia
• pollen cone can be very large
Phylum
Cycadophyta
– seed cones are variable in morphology
• variety in number and shapes
• require very specific pollinators – usually beetles
• seeds contain neurotoxins and should not be eaten
Cycas revoluta pollen cone
Cycas circinnalis pollen cone
seed cone opened
Cycas circinnalis seed cone
• 3 genera of gymnosperms:
• 1. Gnetum - are mostly vines or shrubs
with very broad leaves
– 30 species
– native to southeast Asia, tropical Africa
and the Amazon basin
– seeds are eaten
Phylum
Gnetophyta
• 2. Ephedra – shrubs and bushes
– 40 species
– inhabit desert regions in northern
Mexico and southwestern US
– reduced scale-like leaves
– used in the production of ephedrine
Ephedra sinica
• 3. Welwitschia – only one species
– Welwitschia mirabilis
– deserts of South Africa
– leaves grow perennially – becoming
increasingly longer
– largest leaves in the plant kingdom
Welwitschia mirabilis
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contains a single living species – Gingko biloba
“living fossil”
also known as the “maidenhair tree”
woody tree
broad leaves – very distinct shape
trees are dioecious
– microsporangiate trees
– megasporangiate trees
• no ovulate cones- ovules occur in pairs at the
ends of a short stalked megasporophyll –
unprotected at maturity
• when the female tree produces its seeds –
contain butyric acid which has a putrid odor
Phylum
Gingkophyta
Gingko biloba
Phylum Coniferophyta
• 575 species
• pine trees, firs, spruces, hemlocks, redwoods,
cedars
• 290 million years old
• largest genus – Pinus
– over 100 living species
– predominant in the northern hemisphere
– also planted in the southern hemisphere – only the
Merkus pine occurs there naturally
– world’s oldest known living organism – bristle cone
pine (4,600 years old)
Phylum Coniferophyta: the Conifers
Douglas fir. “Doug fir”
(Pseudotsuga menziesii)
provides more timber
than any other North
American tree species.
Some uses include
house framing, plywood,
pulpwood for paper,
railroad ties, and boxes
and crates.
Pacific yew. The
bark of Pacific yew
(Taxa brevifolia) is a
source of taxol, a
compound used to
treat women with
ovarian cancer.
The
leaves of a
European yew
species produce a
similar compound,
which can be
harvested without
destroying the plants. Pharmaceutical companies are now refining
techniques for synthesizing drugs with taxol-like properties.
Bristlecone pine.
This species (Pinus
longaeva), which is
found in the White
Mountains of
California, includes
some of the oldest
living organisms,
reaching ages of
more than 4,600
years. One tree (not
shown here) is
called Methuselah
because it may be
the world’s oldest
living tree. In order
to protect the tree,
scientists keep its
location a secret.
Sequoia. This giant
sequoia (Sequoiadendron
giganteum), in California’s
Sequoia National Park
weighs about 2,500 metric
tons, equivalent to about
40,000 people.
Giant sequoias are the
largest living organisms
and also some of the
most ancient, with some
estimated to be between
1,800 and 2,700 years old.
Their cousins, the coast
redwoods (Sequoia
sempervirens), grow to
heights of more than 110
meters (taller than the
Statue of Liberty) and are
found only in a narrow
coastal strip of northern
California.
The Conifers
Pollen Cones
microsporangium
• considered to be simple cones
– one single cone axis bearing modified leaves
known as microsporophylls
• cones typically occur in clusters near the
ends of branches
– pollen is liberated to the wind and blown away
• pollen has one cell and two large air
bladders that increase its buoyancy in air
• wind dispersal is inefficient – so few pollen
grains actually land on the ovulate cone
• but conifer forests are very dense
microsporophyll
microsporangium
microspores
(pollen)
Male Pine Cone
Pine pollen cone - microsporophyll
& a microsporangium (containing
microsporocytes).
Microsporangium containing microspores
(pollen)
Microsporangium
With pollen grains
microsporophyll
Pine pollen with male gametophyte
Germinating pine pollen
air bladder
tube
cell
generative cell
(becomes 2 sperm)
Pine pollen with wings
air cells
Seed cones
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more complex than pollen cones
compound cone
each consists of a cone axis with scales
the scales bear leaves that are called sterile bracts in
addition to sporophylls
• scale is a fused megasporophyll with two ovules
• megasporophyll also called an ovulate scale
megasporophyll
sterile
bract
Seed cones
megasporophyll
megaspore
ovules
integument
bract
Pine seed cone with ovulate scale
(megasporophyll) and ovule
megasporophyll
Future ovule
bract
Developing ovulate scale
(megasporophyll) in a young pine
seed cone
female gametophyte
egg nuclei
2 Archegonia (developed from the
megaspore) within the ovule
Archegonia in pine ovule with egg
nucleus
microsporophyll
microsporangium
microspore
(pollen)
Female Pine Cone
Male Pine Cone
The Pinus genus is divided into two subgenera that are separated
by the presence of either one vascular bundle in the leaf
(subgenus Strobus) or two (subgenus Pinus).
Vascular bundle
Vascular bundles
Subgenus Strobus with one
vascular bundle
Subgenus Pinus with two vascular
bundles
Cross Section of a Pine Leaf

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