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Biology 213
Gymnosperms
Introduction
The gymnosperms are tracheophytes that produce seeds but no flowers. The term
gymnosperm means “naked-seed” and refers to the fact that the seeds are produced out in the open
on cone scales and are not enclosed within fruits. The great majority of gymnosperms belong to the
kingdom coniferophyta and include pines, firs, redwood, spruce and many other “Christmas treelike” species. The other phyla of gymnosperms include many less species and at first glance do not
appear to be closely related to the conifers. These phyla are the Cycadophyta, Gnetophyta, and
Ginkophyta. Although the gymnosperms in total do not include many species when compared to the
flowering plants, much of the Earth’s surface is covered by gymnosperms. In the Pacific Northwest,
there are only a few species but conifers dominate almost all of our forests.
Objectives:
1. Know the distinguishing characteristics of the gymnosperms and what distinguishes them
from other plants that we have observed
2. Know and be able to recognize the plants that are looked at today; as well as know to which
phylum they belong
3. Be able to drawn and explain the life cycle of a conifer using correct terminology
4. Continue to improve your scientific sketching and descriptive skills
Coniferophyta, Cycadophyta, Gnetophyta, Ginkophyta
In gymnosperms the gametophyte is highly reduced and lives as a parasite on the sporophyte
generation. When you are looking at a tree you are looking at the sporophyte generation. All
gymnosperms are hetersosporous, i.e., produce two types of spores, mega and microspores. The
sporangia are located on specialized leaves, the scales of the male and female cones. These spores
will then develop into either a female or male gametophyte.
The two distinct types of gametophytes can be found on two different individual
sporophytes (i.e., trees) or more commonly on the same individual sporophyte. If each tree has only
has one type of gametophyte the plant is said to be dioecious (having two houses). If the tree has
both the male and female gametophyte (i.e., two different types of cones on one individual) the
plant is monoecious.
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The Life Cycle of a Conifer
Please look at the diagram of the conifer life cycle and follow along as the life cycle is
described. This diagram shows a monoecious plant, i.e., it produces the male and female cone on
the same tree.
Pollen cones are small and usually found in clumps at the tips of branches. They are not
woody. In the pollen cone, microsporocytes inside a microsporangium undergo meiosis and become
1N. These nuclei then undergo mitosis to form two or more nuclei. This is the highly reduced male
gametophyte and includes the sperm. The male gametophyte is called a pollen grain.
The young female cone (also called the seed, ovulate or woody cone) is also small and often
reddish colored. Inside the megasporangium, a megasporocyte undergoes meiois, producing
megaspores. Three of the megaspore will die leaving one which undergos mitosis and cytokinesis
and develops into a female gametophyte that consists of several hundred cells. The female
gametophyte contains two or more archegonia. Each has a large egg cell surrounded by nutritive
tissue. Surrounding this haploid tissue is the integument. The integument is maternal tissue (2n)
that will later develop into the seed coat.
Pollination occurs when wind blown, or less commonly an insect, transfers pollen from the
male cone to the female cone. The pollen germinates forming a pollen tube that grows toward the
female gametophyte with its archegonia and eggs. When it is close to the archegonia the pollen tube
bursts and sperm swim to the egg and fertilization will occur. In can take anywhere from a year or
more from pollination to fertilization. The zygote then develops into an embryo. In most cases after
a certain amount of development the embryo will go dormant. The integument then dries and
flattens into a winged seed coat. While this is happening the female cone will enlarge and become
woody. This is what most people would recognize as a “pine cone”. When the seed is fully
developed the seed will be released. In some cases the cone will open and the seeds drop out. In
other cases the cone will disintegrate completely. In some instances the cone stays closed and only
release the seeds when opened by fire. When the seed breaks dormancy and germinates it grows
into a new tree.
In some instances the gymnosperm cone is soft and “fruit-like” .Two examples from the
Pacific Northwest are the “berries” on juniper (this is the flavor in gin) and the red “berries” on yew
trees.
Please label the figure of the life cycle of the pine tree with the following terms: mature
sporophyte, germinating seed, young female cone, fully developed female cone, male cone, pollen
grain, microsporangium, microspores, female gametophyte, archegonium, integument. Also show
where meiosis is taking place.
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Pollen and Seed Cones:
Please examine the open seed cone of a pine tree, notice the paired winged seeds or their imprint at
the base of each cone scale. Please examine any other the other cones available, including the
“young” cones. Examine the pine seeds.
Please look at the prepared slide of the male pollen cone. Examine it at low power first to become
oriented and observe the scales. Examine one microsporangia at higher power. You should be able
to see many individual pollen with their “Mickey Mouse ears”. Please make a drawing at 40X and
400X.
Conifer Branches and Leaves:
Please examine the conifers branches that are available. Most, but not all conifers have evergreen
leaves. This means that instead of losing all their leaves at the same time every year they only lose a
few leaves at a time. In the Pacific Northwest we have two different species of larches that are
deciduous and lose their leaves every fall. Leaves of the conifers are modified into needles or scales
and are often covered with waxy material to prevent dehydration.
Please draw two different conifer branches paying close attention to the number of needles in each
bunch or the arrangement of the scales. You will be told which conifers you will need to be able to
recognize.
Other Gymnosperms:
Please examine the other gymnosperms that are available. Do they look closely related to a pine
tree?
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Please answer the following questions.
Name______________________
1) What are tracheophytes? We have already investigated the life cycle of another plant that was a
tracheophyte. What is its common name?
2) If an individual plant has both male and female gametophytes is is it monoecious or diecious?
3) In what structure is the female gametophyte found?
4) Are the scales of a conifer cone haploid or diploid?
5) The male gametophyte is commonly called a ________________________________.
6) The archegonium is part of the gametophyte/sporophyte.. It houses the egg/sperm. (Please circle
the correct answers.)
7) What is the difference between fertilization and pollination?
8) A conifer seed contains cells from two different generations. Explain.
Please staple any drawings and diagrams that you made/labeled and hand in this page.
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