Gymnosperms
Gymnosperm
Facts
- The late tracheophytes
are the Gymnosperms
and Angiosperms.
Gymnosperms and
Angiosperms are the
Seed Plants.
- Gymnosperms bear
cones and have naked
seeds. The seeds are
termed “naked”
because they are not
enclosed by fruit as in
the angiosperms.
Giant Sequoias
- Seeds are exposed on modified leaves that form cones.
- Gymnosperms are heterosporous. They have pollen and seeds and almost all
gymnosperms are woody.
- Gymnosperms depend on wind for pollination.
- Gymnosperm Examples: pines, firs, redwoods, junipers and sequoia.
A Cladogram of the
Gymnosperms.
Division Coniferophyta
Division Gnetophyta
Division Ginkgophyta
Division Cycadophyta
Gymnosperm Evolution
Gymnosperms were the first seed plants to
appear-millions of years before the first
angiosperms. The conifers replaced many
ferns as Earth's climate became more arid
because conifers are better adapted for a dry
environment. These modifications for a dry
environment include needle-shaped leaves,
which have a thick, protective cuticle and a
relatively small surface area. Seed and
pollen found in gymnosperms are key
reproductive innovations for life on land
(water is not necessary for sperm to reach
egg like in the early tracheophytes).
Division Cycadophyta – The Cycads
Cycads were very important in
the Mesozoic Era. The were
important for herbivorous
dinosaurs. Today, they are
not so diverse. They are
palm-like.
Sago Palm (Cycas revoluta)
Zamia sp. with ovulate (seed) cones.
Division Ginkophyta – The Ginkgo
Only 1 living species, the ginkgo tree. It tolerates pollution and is an urban street
tree. Ginkgo is dioecious. Pollen trees are preferred. The fruit of seed trees smell
really bad. So what would plant in your yard, a male or female tree?
Ginkgo Tree (Ginkgo biloba)
Also known as the madenhair tree.
Division Gnetophyta – Gnetum, Welwitchsia, Ephedra
These gymnosperms have vessel elements like the flowering plants.
Welwitschia mirabilis
Division Coniferophyta (Pinophyta) –
The Conifers “Cone-bearers”
- Many conifers have woody cones. Pine is an example of this.
- Some lack woody cones and have a berry-like tissue around seeds.
Eight families are
found in this
division.
The pine family
(Pinaceae)
includes the pines,
fir and spruce.
Fascicles of needles born or short shoots from a pine (Pinus sp.).
Gymnosperm Reproduction
Each individual tree generally has both cone types
(male and female). Therefore these trees are
monoecious.
Small pollen cones produce microspores that develop
into male gametophytes or pollen grains. Larger
ovulate cones usually develop on separate branches
of the tree and produce megaspores that develop
into female gametophytes.
Strobilus (plural, strobili) – a number of modified
leaves (sporophylls) or ovule bearing or pollen
bearing scales grouped together on an axis; papery;
pollen is produced here; part of pollen cone.
Pollen grain is the immature male gametophyte.
Ovulate cone (female) – when young it is softer and
smaller than the male strobilus.
Pollination replaces the need for free water, which is
necessary in early tracheophyte reproduction.
Mature Ovulate
(female) cones
of Shasta red fir.
Cones in this
genus are borne
upright. Note
the long bracts
projecting
beyond the cone
scales.
Douglas Fir (Pseudostuga menziesii)
with soft needles and cone.
Pollen (Male) Strobili
A cluster of strobili near the end of a
branch at the time of pollen release.
A longitudinal
section of one
strobilus,
showing
microsporangia
attached to the
underside of each
scale.
Each microsporangium is
filled with pollen grains;
the pollen grains consist
of only 2 cells; each with
its own nucleus.
Ovulate (Female) Cones at Time of Pollination
2- Month-Old
cones at the
tip of a young
branch.
Below are
large cones
just older than
1 year.
The mature open cone is 2 years
old when seeds are mature.
A closer view of one ovule (dashed
area). Note the large megasporocyte
inside the nucellus and the micropyle
and micropylar chamber. Meiosis has
not yet occurred.
Longitudinal
section
through a 2month-old
cone, showing
ovules on top
of each scale.
Life Cycle of Pine
A Representative Gymnosperm.
(a) A young ovulate (seed)
cone.
(b) A scale from an ovulate
cone with 2 ovules on its
upper surface.
(c) Longitudinal section of an
ovulate cone at the time of
pollination.
(d) A pollen strobilus
(e) One scale from a pollen
strobilus
(f) A section of a
microsporangium with
mature pollen grains inside.
(g-i) A developing male
gametophyte.
(c,j,k) A developing female
gametophyte.
(l-n) A developing seed.
(o) Germination of the seed.
Ecological and Economic
Importance of Gymnosperms
The gymnosperm landscape covers the 1/3 of
the landmass of North America.
The presence of gymnosperms can cause
acidic or nutrient poor soil by presence of
decaying pine needles.
The harvesting of ponderosa pine, eastern
white pine and Douglas fir is important to the
forestry economy.
BIO 141 Botany with Laboratory
•
This product is sponsored by a grant awarded under the President’s Community-Based Job Training Grants as implemented by the U.S. Department of
Labor’s Employment and Training Administration. The information contained in this product was created by a grantee organization and does not
necessarily reflect the official position of the U.S. Department of Labor. All references to non-governmental companies or organizations, their services,
products, or resources are offered for informational purposes and should not be construed as an endorsement by the Department of Labor. This product
is copyrighted by the institution that created it and is intended for individual organizational, non-commercial use only.