Gymnosperms

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Gymnosperms
Four major living groups. Cycads (Cycadophyta),
Welwitschia group (Gnetophyta), Ginkgo, the
Maiden Hair Tree (Ginkgophyta), and the
conifers (Pinophyta) .

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Cycads
Cycas bougainvilleana
Cycads resemble palms or tree-ferns in overall
appearance but differ greatly in detailed
structure and reproductive behaviour. Cycads are
dioecious (i.e. male and female reproductive
structures are borne on separate plants), and
reproduction is by seeds produced on open
carpophylls or seed-bearing leaves. Although
technically woody plants, unlike other woody
plants, cycads have a thick, soft stem or trunk
made up of mostly storage tissue with very little
true wood. The living cycads include about 250
species, with 11 genera in 3 families.
Microcycas calocoma Photo Dennis Stevenson
Female cone
Cuban species
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Welwitschia mirabilis
Gnetophyta
Large, straplike leaves that grow continuously
along the ground. During its entire life, each
plant produces only two leaves, which often split
into many segments as a result of the leaves
being whipped by the wind. Carbon-14 datings of
the largest plants have shown that some
individuals are over 1500 years old.
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Ginko biloba
There are no native ginkgoes living in the wild.
Several ginkgoes were the only living survivors
of the atomic bomb blast at Hiroshima
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The Evergreen State
Why is Washington called the
Evergreen State?
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Most conifers are evergreen
Evergreens have potential for growth all-year
round
What is the advantage of the potential for all
-year round growth?
Why arent all plants evergreen?
What is the advantage of the deciduous habit
over the evergreen habit?
Why is so much of Washington covered by
evergreen conifers?
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Evergreenness
What is the advantage of the potential for all
year round growth?
Opportunistic growth when conditions may be
favorable and lack of dependence upon a
particular time when growth must be made.
Why arent all plants evergreen?
Evergreen plants are frequently slow growing.
The features that enable them to survive harsh
conditions do not always enable them to grow
quickly.
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What is the advantage of the deciduous habit
over the evergreen habit?
Deciduous plants are frequently faster growing
than evergreen plants and can rapidly exploit
favorable and reliable habitats. Leaves do not
require to withstand severe cold and leaf
abscission enables nutrients and carbohydrates to
be withdrawn into the plant for re-use
Why is so much of Washington covered by
evergreen conifers?
It regularly has periods of summer drought but
mild wet winters. This can favor evergreens over
deciduous trees.
In what other type of environment are evergreen
conifers frequently found?
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Time scale
Relative numbers of species of major groups of
plant across geological time
Angiosperms
Gnetales
Cycads
Mosses
Ferns
Ginkgos
Conifers
Origins of conifers in the Permian
The coal forming period
Millions of years
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Pangea
Gymnosperms show adaptations to drier conditions
than mosses and ferns both in their reproduction
and vegetative growth
Continental type climates typically have dry
periods or seasonal rains. These can be
seasonal and may be called monsoons
In the Permian the land masses came together and
formed a large continent call Pangea
Carboniferous
360 to 286 mya
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Adaptations for the drier environment
Reproductive
1.      Airborne male gametophyte (pollen)
carried by wind to the female gametophyte where
sperm fertilizes the egg located in the female
gametophyte in the ovule which is retained,
sustained and protected by the sporophyte.
2.      Production of a durable seed that at
maturity consists of a protective seed coat, a
source of nutrition and an embryo sporophyte all
in one package.
Vegetative
3. Seed plants have wood producing tissue well
developed in some species for water conduction
and support. This enables plants to grow tall
and out-compete neighbors
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Reproduction in the conifers
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The cone is a modified branch. Unlike the flower
it does not have sepals or petals. Usually
separate male and female cones are borne on the
same plant, i.e., monoecious. Each of the
numerous scales, or sporophylls, of the male cone
bears pollen and each female cone scale bears
ovules in which egg cells are produced. .
http//forest.wisc.edu/forestry415/INDEXFRAMES.HTM
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Life cycle
Fig. 17.8
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From ovule to seed
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Cedrus deodora
The diminutive female cone
Male cones all lined up and ready to go!
Developing seed cones
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Pictures of male cone and pollen
Continuing vegetative shoot
Pollen grains
Male cone
Microsporangium
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Pictures of female cone
Female gametophyte
Archegonia
Egg
Megagametophyte
Ovule
Single scale (sporophyll
Longitudinal section through ovulate cone
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Bristlecone pine
Pinus longaeva
Male cone
Current year
Last years empty sporangia
Female cone
The oldest aged specimen is 5,600 y
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Sections you need to have read
17.8 and Introduction to Chapter 31
Courses that deal with this topic
ESC 200 Trees in Our Environment
ESC 221 Dendrology and Autecology