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Plant Diversity and Evolution
Part 3
Gymnosperms
Poland’s pine crooked forest (man made)
Outline
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Introduction
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Phylum Pinophyta – The Conifers
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Other Gymnosperms
•
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Phylum Ginkgophyta – Ginkgo
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Phylum Cycadophyta – The Cycads
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Phylum Gnetophyta – The Gnetophytes
Human Relevance of Gymnosperms
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Conifers
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Other Gymnosperms
Introduction
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Gymnosperms are vascular plants that produce seeds.
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These are the oldest known seeds (late Devonian, more
than 350 million years ago) but it is widely accepted that
Gymnosperms evolved in the Carboniferous period.
•
The first seed plants were
fernlike in appearance and
for a long time were
classified as pteridosperms
(seed ferns) today, these
have been reclassified as
gymnosperms (in the cycads
group)
Adaptations that appear
in Gymnosperms
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Plants can live without being so dependent on water.
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Instead of spores, plants developed pollen (so fertilization
can occur without water)
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Seeds: The production of a seed protected by a seed coat
lets the embryo be transported and developed elsewhere.
The evolution of the seed
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Seeds provide a significant adaptation for
plants on land.
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Protective seed coat
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Supply of food for embryo
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Capable of dormancy in unfavorable
environmental conditions
Gymnosperms Characteristics
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Xylem has only tracheids (except the Gnetophyta). Soft
woods.
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Deep root systems
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Leaves like needles, scales or flat thin surfaces (a few
exceptions)
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There are seed bearing plants, but they do not have
flowers, they have reproductive structures known as
strobilus/strobili or cones. They can be dry or fleshy.
Gymnosperm
Angiosperm
Characteristics, continued
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Wind pollinated.
•
Wind dispersed seeds
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In angiosperms, the seeds
are produced after
fertilization inside an
enclosed ovary. In
gymnosperms, the ovule is
exposed. The term
gymnosperm means
“naked seed”
The Female Cone
•
Inside the female cone,
we find ovules. These
ovules are exposed.
•
Inside the ovules, we
find the female
gametophyte or
nucellus (in
angiosperms, this was
known as the embryo
sac).
•
Inside the nucellus, we
find the egg cell
(megaspore).
The Male Cone
•
Pollen cones produce pollen grains
Gymnosperm vs. Angiosperm
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In angiosperms, the seeds are
produced after fertilization
inside an enclosed ovary (see
apple).
•
In gymnosperms, the ovule is
exposed, thus the seed is also
exposed (Gymnosperm refers
to the exposed nature of the
seeds.
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Gymnosperms classification
Four living phyla
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Pinophyta: It bears distinct strobili (cones), needlelike
leaves arranged in clusters. There are about 600
species of pines, firs, spruces, cedars, araucaria
(monkey tree), etc…
•
Ginkgophyta: Real leaves, notched, broad, fanshaped leaves with evenly forked veins. Plum like
seeds enclosed in fleshy covering. One single living
species, Ginkgo biloba
•
Cycadophyta: Cross between tree fern and palm.
The strobili (cone) is in the center. There are about
300 species
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Gnetophyta: Vessels and tracheids in xylem. About
70 species
Phylum Pinophyta. The Conifers
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The conifers, division Pinophyta, also known as division
Coniferophyta or Coniferae.
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The total number of species is relatively small (a total of 65–
70 genera and 600–630 species), conifers are of immense
ecological importance: They are the dominant plants over
huge areas of land, especially the boreal forests of the
northern hemisphere, and in similar cool climates in
mountains ecosystems.
•
The Podocarpaceae (a family of conifers) are a large family
of mainly Southern Hemisphere conifers. The family is a
classic member of the Antarctic flora ( Australasia,
particularly New Caledonia, Tasmania, and New Zealand,
and South America (primarily in the Andes mountains).
Phylum Pinophyta. The Conifers
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Species of Phynophyta includes cedars, Douglas-firs,
cypresses, firs, junipers, kauri, larches, pines, hemlocks,
redwoods, spruces, and yews.
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Pines (Pinus) is the largest genus and the dominant trees in
coniferous forests of Northern Hemisphere.
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Include world’s oldest known living organisms: Bristlecone
pines.
Pinus longaeva, White Mountains, eastern
California. 5065 years old. Tom Harlan research.
Who is older?
•
Extra Credit. Who is older Pando or species of Pinus
longaeva?
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Who/What is Pando? Explain the nature of Pando and why
would you consider Pando or Pinus longaeva older?
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Explain botanically the details and discuss with wellsupported arguments what is your opinion in favor of one
or the other.
Phylum Pinophyta. The Conifers
Leaves needlelike and arranged in clusters
(fascicles) of two to five needles.
The needles have modifications that enable
them to survive harsh conditions. These
includes:
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Hypodermis located below the
epidermis. One to two layers of thickwalled cells.
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Thick cuticle
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Recessed or sunken stomata
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Resin canals. Resin is antiseptic and
aromatic, prevents development of
fungi, and deters insects.
Pines Reproduction
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Seed cones (female) larger than
pollen cones.
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The female cone has a pair of ovules
at bases of seed cone scales.
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Pollen cones (male strobili) consist of
papery or membranous scales.
The Female Cone
•
Inside the female cone,
we find ovules. These
ovules are exposed.
•
Inside the ovules, we
find the female
gametophyte or
nucellus (in
angiosperms, this was
known as the embryo
sac).
•
Inside the nucellus, we
find the egg cell
(megaspore).
The Male Cone
•
Pollen cones produce pollen grains
Reproduction cont.
Seed cones take two years to mature.
First year:
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Pollen grains catch on sticky pollen drops oozing out of micropyle (ovule
opening).
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Pollen grain produces pollen tube that grows through nucellus. Two sperms
produced in pollen tube.
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Ovule develops.
Second year:
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Female gametophyte inside the ovule and archegonium mature.
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Pollen tube arrives at archegonium.
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One sperm unites with egg, forming zygote. Other sperm degenerates.
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Embryo nourished by female gametophyte.
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Integument becomes seed coat.
Pine Reproduction:
Phylum Ginkgophyta
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Phylum Ginkgophyta – Ginkgo
(maidenhair trees). Only one
living species and it only exists in
cultivation.
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Notched, broad, fan-shaped leaves
on short, slow-growing spurs.
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No midrib or prominent veins.
Hair-like veins branch
dichotomously.
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Deciduous
Phylum Ginkgophyta
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Life cycle similar to pines but male
and female structures on separate
trees.
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Seeds enclosed in fleshy seed coat
with nauseating odor.
Male strobili (cones)
Seeds and leaves
Phylum Cycadophyta – The Cycads
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Slow-growing plants of tropics and subtropics
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Tall unbranched trunks
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Crown of large pinnately divided leaves
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Life cycle similar to conifers. Male and female
plants. Pollination sometimes by beetles.
Male cycad
Female cycad
Phylum Gnetophyta
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Unique among the gymnosperms in having vessels in the
xylem.
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Ephedra: Shrubby plants of drier regions of southwestern
North America.
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Welwitschia: Only one species, confined to deserts of southwestern
Africa.
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Gnetum: Vine-like plants with broad leaves confined to the tropics
Human Relevance of Gymnosperms
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Conifers
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Lumber: Masts in sailing vessels, crates, boxes, matchsticks,
furniture, telephone poles, railroad ties, mine timbers, building
lumber.
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Paper making
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Turpentine and rosin (both from resin)
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Fuel.
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Edible inner bark and needles of white pine, and seeds of nearly
all pines
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Ornamentals
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Pharmaceuticals (taxol for ovarian cancer from yew trees)
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Other Gymnosperms
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Ginkgo:
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Seeds for food (after seed coat
removal)
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Ginkgo extracts to increase blood
circulation
Ephedra: Drug ephedrine for
respiratory problems from a Chinese
species
Review
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Introduction
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Phylum Pinophyta – The Conifers
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Other Gymnosperms
•
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Phylum Ginkgophyta – Ginkgo
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Phylum Cycadophyta – The Cycads
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Phylum Gnetophyta – The Gnetophytes
Human Relevance of Gymnosperms
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Conifers
•
Other Gymnosperms