UNIVERSITY OF MAIDUGURI

(FACULTY OF LIFE SCIENCE)

DEPARTMENT OF BOTANY

COURSE CODE: BOT 203

COURSE TITLE: HIGHER PLANTS

TWO (2) UNITS

TOPIC: GYMNOSPERMS
CONTENTS

• Background
• Characteristics
• Morphology
• Reproduction
• Classification
• Relationship
• Economic importance

OBJECTIVES

• To be able to define gymnosperms

• Identify gymnosperms using their general characteristics
• Differentiate between the various classes of gymnosperms
• Know the morphology and reproduction of gymnosperms
• Understand the affinities and relationships of gymnosperms
• Know the economic values of gymnosperms

1. BACKGROUND AND DEFINATION OF GYMNOSPERMS

The evolution of plants has resulted in widely varying levels of complexity, from the earliest algal
mats, through bryophytes, lycopods and ferns, to the complex gymnosperms and angiosperms of
today. The dominant groups today are the gymnosperms, which include the coniferous trees, and
the angiosperms, which contain all fruiting and flowering trees. Both groups arose from within the
pteridosperms, probably as early as the Permian. The first spermatophytes (“seed plants”), the first
plants to bear true seed – are called pteridosperms (“seed ferns”). Their foliage consisted of fern-
like fronds, although they were not closely related to ferns. Most of gymnosperms incase their
seeds in a woody cone or fleshy aril but none of them fully enclose their seeds.

All gymnosperms are woody plants. Their stems are similar in structure to woody dicots, except
that most gymnosperms produce only tracheids in their xylem, not the vessels found in dicots.
Gymnosperm wood also often contains resin ducts. According to the height of the plant, we classify
them into:
1. Trees: Plants with ligneous stems, with a superior height of 5 meters. In the case we call the
stems trunks. They do not generally branch up to a considerable distance from the soil.

2. Shrubs: They are those plants with ligneous stems from 1 to 5 meters tall. In this case, branching
begins at the soil level.

3. Bushes: Ligneous plants - shorter than 1 meter tall.

4. Herbaceous plants: They have non-woody short stem and

The name gymnosperm is derived from two Greek words gymnos, meaning "naked", and
sperma, meaning "seed". The name refers to the exposed nature of the seeds, which are produced
on the surface of sporophylls or similar structures instead of being enclosed within a fruit as they
generally are in the flowering plants. The word Gymnosperm, was first used by Theophrastus, a
pupil of Aristotle in his famous book “Enquiry into Plants”. He used this term in all those plants
having unprotected (without covering) seeds. The ovules of gymnosperms are freely exposed
before and after fertilization while in case of angiosperms where the ovules are enclosed within
the carpel.

2. CHARACTERISTICS OF GYMNOSPERMS

1. Gymnosperms are, those seed plants in which the seeds remain exposed over the surface
of the megasporophylls because they are not folded to form pistils.
2. Gymnosperms are a small group of seed plants which are represented by only 900 living
species.
3. Gymnosperms are more ancient than the angiosperms. They formed dominant vegetation
on earth some 200 million years back in mesozoic era.
4. They are slowslow growers and lacks vegetative means of reproduction.
5. All gymnosperms are perennial and woody, forming either bushes or trees.
6. Some gymnosperms are very large and live for thousands of years, e.g., Sequoia
sempervirens (tallest gymnosperm of 111.6 m) Zamia pygmia is smallest (26 cm).
7. Flowers are absent.
8. They have two types of sporophylls, microsporophylls and megasporophylls. These are
usually aggregated to form distinct cones or strobili. The pollen cones (male cones) and
seed cones (female cones) respectively.
 9. Seeds do not occur inside a fruit they are naked.
10. A distinction of ovary, style and stigma are absent.
11. Ovules are orthotropous and sessile each surrounded by a 3-layered integument.
12. Female gametophyte contains archegonia.
13. Pollination is direct as a stigma is absent and the pollen grains directly reach the micropylar
ends of ovules. Pollination is usually accomplished by wind (anemophily).
14. Male gametophyte produces only two male gametes or sperms, generally one of them is
functional.
15. An external water is not required for transport of male gametes. Instead, a pollen tube is
formed by the male gametophyte for effecting fertilization (siphonogamy).
16. Seeds contain a food laden tissue or endosperm for future growth of embryo into seedling.
The tissue represents the female gametophyte.
17. Like pteridophytes, xylem does not possess vessels except in some gneophytes.
18. Phloem is without companion cells and sieve tubes. Sieve cells are not arranged end to end
in rows.
19. Vascular tissues are arranged into vascular bundles just like angiosperms.
20. Vascular bundles of stem are open so that secondary growth is quite common.

3. MORPHOLOGY OF GYMNOSPERM

Stem

• The stem may be aerial, erect, unbranched (e.g. Cycas, Zamia) or branched (e.g. Pinus,
Cedrus etc.).
• In gymnosperms the branches may be of two types on the basis of their branching system.
The long shoots and the dwarf shoots.

Leaf

• Gymnosperms bears both microphyllous and megaphyllous leaves.

• The microphyllous leaves are and well developed.
• The leaves may be simple or compound and vary in shape, size and form, as a minute scale
leaf to several feet long megaphylls (e.g. in Cycas).
 • Gymnosperms show great diversity in leaf venation, it may be parallel, reticulate or even
dichotomous.
• The leaves are always evergreen and mostly possess resin canals as in Pinus, Cedrus and
Abies.
• The arrangement of leaves may be whorled (Cedrus), opposite or decussat (Gnetum,
Ephedra etc .) or spirally arranged (Taxus, Podocarpus etc .).
• Conifers usually have sunken stomata.
• The shape of leaves may also vary from triangular (Pinus roxburghi ), semi -circular (Pinus
sylvestris ), bifid or circular (Pinus microphylla), and bifacial leaflet of Cycas zamia, and
Gnetum leaves.

Wood

• Due to secondary growth gymnosperms possess primary and secondary wood.

• The secondary wood is the characteristic feature of cycadophyta.
• The wood is porous, soft and more parenchymatous in nature, while pycnoxylic wood is
the characteristic feature of coniferophyte.
• The wood is compact and narrow medullary rays, xylem lacks wood vessels except in
Ephedra, Gnetum etc.
• The xylem is usually endarch or mesarch in stem while it may be exarch in roots.
• The vascular bundles are conjoint, collateral, endarch and open in gymnosperms.

4. REPRODUCTION IN GYMNOSPERMS

Gymnosperms possess two different types of spores and hence refers as hetrosporous. The
microspores are smaller while another spore larger in size called megaspore. These two kinds of
spores on germination produce two different kinds of gametophytes. The microspore or pollen
grains produce male gametophyte, while the larger megaspore produces female gametophyte,
bears two or more archegonia or female sex organs. These spores are produced within the leafy
structures or sporangia that borne on sporophylls, spirally arranged along an axis to form compact
strobili or cones.

The microsporangiate or male strobili bearing microsporophyll and microsporangia while the
megasporangiate or female strobili bear megasporophylls with ovules or microsporangia. The two
types of cones or strobili may be borne on same tree as in Pinus or on different trees like in Cycas
and Ginkgo. The microsporangium contains numerous small microspores whereas the
megasporangium contains only one larger megaspore. Both the spores i.e., microspore and
megaspores are haploid and develop as a result of meiosis or reduction division in the respective
spore mother cells. They are the primary structures of the male and female gametophytes
respectively. In gymnosperms the gametophytes are endosporic i.e., they develop within or inside
the respective spore wall. In general, the strobili or cones are of varying shapes and sizes in
different species. Their position also varies from plant to plant. Among gymnosperms, the
microsporangiate or male cones are large stand arises at the apex of male plant.

Pollination and Fertilization

In gymnosperms the medium of pollination is wind; it results in the transfer of semi-germinated

pollen grains on the micropyle of the ovule. In most of the gymnosperms, the pollen grains are
caught in to a pollination drop selected by micropylear end of the ovule. After drying of pollination
drop the microspores in semi-germinated stage are drown in to the ovule. Just after the drawing of
the microspores in the microgametophyte the micropyle closes. A distinct pollen chamber is
formed at the apex of the nucellus and receives the micro-gametophytes on pollination as in some
gymnosperms (Cycas, Ginkgo, Ephedra etc.) While in Conifers and other gymnosperms the semi-
germinated pollen grains come in direct contact with the nucellus beak. Contrary to this in the
palaeozoic gymnosperms now extinct the pollen chambers contained liquid filled cavities in which
the motile sperms were liberated due to the dehiscence of the microspore wall. In general, in all
the living gymnosperms, the microspores by division produce pollen tube as a tubular outgrowth
that grows through the nucellar tissue for several months in to the nucellar tissue and absorb food
and supply it to the microgametophyte at the grain end or at the lower end of the pollen tube. The
pollen tube bursts during fertilization and liberation of multiciliate male gametes along with some
liquid in the cavity above the megagametophyte. At that time the sperms swims to the archegonial
neck and enters into the archegonia and only one of them fuses with the egg or oosphere and form
the diploid zygote or oospore.

In the conifers the pollen tube plays an important role of sperm carrier. The male gamete along
with stalk and tube nucleus migrate to tip of the pollen tube. The tube grows through the nucellar
tissue, reaches to the archegonial tube enters through it and after bursting liberates the male
gametes. Among them, one fuses with the egg to form a diploid zygote. This specific process of
fertilization is termed as Siponogamous. However, in Cycad of ilicales, Bennettitales and
Cordaitales, (the extinct orders of gymnosperms) did not produce pollen tubes and sperms were
liberated directly into the pollen chamber. This process is known as Zooidogamous.

Seed Formation

After fertilization, the structure developing from fertilized ovule and its consequent enlargement
is known as seed. The zygote develops into an embryo while the endosperm persists as a nutritive
tissue, whereas the nucellus becomes disorganize (or serves as nurse cells for developing embryo)
or it may remain in the form of dry tissue at the micropylar end of the seed known as nucellar cup.
In gymnosperms the inner fleshy layer called the tegmen, may persist as a thin layer of seed coat.
The middle stony layer later changes into a hard layer called the testa, which mechanically
protected the female gametophyte and the embryo. Development of seed may vary in different
species of gymnosperms. In Cycas and Taxus the outer fleshy layer develops into scarlet red and
fleshy outermost seed coat. In Gnetum the seed develops before the embryo complete its
development. In Taxus a fleshy aril develops from the basal cup-shaped structure. Except Cycas
and Ginkgo, the seeds of all gymnosperms remain dormant for some time. While in these two
genera the seeds germinate immediately, they lose their viability when fall on moist substratum.
In gymnosperms the seed represents two sporophytic and one gametophytic generation. Different
parts of a seed of gymnosperms represent different generations.

• The young embryo represents the new sporophytic generation.

• The seed coat represents the old sporophytic generation.
• The endosperm represents the gametophytic generation.

In most of the genera of gymnosperm the germination of seed is epigeal means the cotyledons
come above ground except in Ginkgo where the cotyledons remain embedded in the endosperms.
While in Ephedra trifurcate Vivipary has been reported. All the gymnosperms represent
heterogenous alternation of generation.

5. CLASSIFICATION OF GYMNOSPERMS

In older times gymnosperms were kept among angiosperms. It was Robert Brown (1827) who first
of all recognized these plants due to presence of naked ovules and placed them in a distinct group
called gymnosperms. Bentham and Hooker (1862-83) in their ‘Genera Planterum’ placed this
group in between dicotyledonae and monocotyledonae. The classification of gymnosperms is quite
controversial because several genera and a few orders like the cordiatales and cycadeoidales are
known only in fossil state. Attempts have, however, been made from time to time to classify them.
Four phyla of living gymnosperms are recognized.

1. Phylum Pinophyta: includes about 575 species of coniferous woody plants. Fossils of
some conifers extend back 290 million years.
2. Phylum Gnetophyta: includes three genera of gnetophytes that have wood with vessels-
a structural element.
3. Phylum Ginkgophyta: has a single living representative, Ginkgo, which has fan-shaped
leaves, and seeds enclosed in a fleshy covering.
4. Phylum Cycadophyta (Cycas): includes the palm-like cycads

Characteristic Features of pinophyta

• Mostly evergreen with branched stems, rarely shrubs.

• The leaves are needle or scale-like, sometimes flattened, rarely falling in autumn, spirally
arranged or whorled.
• The leaves possess xerophytic characters.
• Wood without vessels consisting of long tracheids which show bordered pits.
• Presence of resin canals frequently.
• The flowers are monoecious or dioecious.
• The female flowers are terminal or lateral and then surrounded by supporting bracts.
• The male flowers consist of a number of stamens arranged in strobili.
• The stamens are usually many, each with 2 to 20 pollen sacs, connective often produced as
an appendage.
• Pollen grains may be winged, e.g., Pinus.
• The female flowers are arranged in cones or catkins with the exception of Taxaceae,
Cephalotaxaceae and Podocarpaceae.
• Each female flower consists of a bract (sterile) and a scale (fertile).
• The scale is found above the bract.
 • The ovules develop on the upper surface of ovuliferous scales.
• The female cone ripens in 1-3 years and is usually dry on ripening.
• The seeds are often winged, nut like and with a leathery or woody testa.
• The cotyledons are epigeal and 2-16 in number.
• Polyembryony is quite common.
• They produce non-motile sperms at the time of fertilization.
• Examples: Pinus sp., Picea sp., Juniperus sp., Cupressus sp., Podocarpus sp., Taxus sp.,
Abies sp., Sequoia sp., Taxodium sp. Etc.

Characteristic features of Gnetophyta

• These are woody plants, of which some species are trees (Gnetum gnemon)
• Some are lianes or shrubs and a few are stumpy turnip-like (e.g. Welwitschia mirabilis).
• Leaves are simple elliptical or strap-shaped or sometimes reduced to minute scales.
• They are generally opposite or whorled.
• Vessels are present in the secondary wood.
• Flowers are unisexual, usually dioecious and only rarely monoecious.
• Flowers are arranged in compound strobili or ‘inflorescences.
• The male flowers are surrounded by a perianth.
• Each male flower contains an antherophore with one to eight synangia.
• A single erect orthotropous ovule is present in each female flower.
• Nucellus of the ovule remains surrounded by two or three envelopes.
• The micropyle of each ovule remains projected in the form of a long bristle-like tube.
• At the time of fertilization, the pollen tube contains two male nuclei.
• A unicellular primary suspensor is present in the embryo.
• Two cotyledons are present in the embryo.
• Gnetum sp., Welwitschia sp., Ephedra sp.

Characteristic features Ginkgophyta

• Ginkgo is an attractive tree of pyramidal form.

• It is about 30m tall with fan-shaped, deciduous leaves.
• There are two types of shoots (shoot dimorphism) in Ginkgo.
 • Long shoots or shoots of unlimited growth which elongate rapidly and bear scattered
leaves.
• The spur or dwarf shoots or shoots of limited growth with a cluster of leaves at the apex.
• The long shoot grows fast, nearly half a meter in one year.
• The dwarf shoots arise in the axils of leaves on long shoots.
• The leaves change their colour to golden yellow before they are shed in autumn.
• They are so much like those of Adiantum both in form and venation that the name maiden-
hair tree.
• The young root is usually diarch.
• Secondary growth takes place as usual, but the annual rings are not so conspicuous as in
the stem.
• The leaves on the dwarf shoots are entire with a wavy margin, but those on long shoots
have a conspicuous apical notch which is sometimes very deep making it bilobed, hence
the specific name biloba.

Characteristics of Cycadophyta

• They comprise a group of the plants with a number of primitive characters than are
possessed by any other group of living gymnosperms, and because of the retention of these
primitive characters sometimes they are supposed to be ‘the living fossils.
• All cycads are typical xerophytes.
• The plants are low and palm-like in habit.
• The stem is short, un-branched, columnar and covered with dense persistent leaf bases.
• The leaves are pinnately compound and arranged in a terminal crown.
• The plants grow very slowly but they live for ages.
• Comparatively the pith is large and cortex is broad.
• There is a narrow zone of conducting tissue.
• The cycads are strictly dioecious, i.e., micro and megasporophylls develop on separate
plants.
• Except the female strobilus of Cycas the sporophylls are arranged in definite cones.
• The ovules are straight and usually sessile. The pollen chamber is found for receiving the
pollens.
 • Male gametes are motile.

6. RELATIONSHIP OF GYMNOSPERMS WITH OTHER PLANTS

Gymnosperms occupy a place in between pteridophytes and angiosperms in the plant kingdom.
Therefore, gymnosperms bear close affinities with the pteridophytes on the one hand and the
angiosperms on the other. In many other characters they differ from both.

Resemblances or Similarities with Pteridophytes:

• Sporophytic, independent plant body is present in both the groups.

• It is differentiated into root, stem and leaves.
• Sporophyte possess a well-developed vascular tissue.
• Xylem lacks vessels and phloem companion cells.
• Young leaves show circinate vernation.
• Presence of megaphyllous leaves.
• Gymnosperm and few pteridophytes e.g. Selaginella are heterosporous i.e. form micro-
and
megaspores in micro- and megosperangia, borne on the micro and megasporophylls
respectively.
• In Cycas, sporangia are grouped in sori like pteridophytes.
• The female sex organ is archegonium in both the groups.
• The male gametes of Cycas and Ginkgo are motile like the pteridophytes.
• Permanent retention of megaspore within the megasporangium.
• Gametophytes are endosporic and highly reduced.
• Female prothallus develops before fertilization and there is free nuclear division.
• Germination of spores is precocious in gymnosperms and hetrosporous pteridophytes.
• Development of distinct embryo after fertilization.
• Like the pteridophytes, gymnosperms show marked alternation of generation between
gametophytic and sporophytic phase.
• Sporophytic generation or sporphytic phase is dominant, independent and large at maturity
while the gemetophtic generation exhibits progressive reduction and dependence.
 Difference between Gymnosperms and Pteridophytes

GYMNOSPERMS PTERIDOPHYTES
Xerophytic habitats. Hygrophytes
Taproot. Adventitious roots
Eustelic organization. Absent
Secondary growth Absent
Aerial Stems Underground rhizomes.
Only microspores are shed from microsporangia. Both micro- and megaspores are shed from
sporangia.
Pollen tube present Pollen tube is absent
Archegonia lack neck canal and neck canal cell Neck canal and neck canal cells are present.
Ovule is present Ovule is absent
Water is not essential for fertilization. Water is essential for fertilization.
Gametophyte is fully dependent on sporophyte. Gametophyte is green and autotrophic.
Presence of free nuclear divisions Absent
Seeds are present. Absent
Similarities with Angiosperms

• Main plant body is sporophytic and is differentiated into root, stem and leaves.
• Plants are trees or shrubs and may be erect or climbing.
• Root system is well developed and the roots may be diarch, triarch, tetrach or polyarch.
• The xylem is exarch in the roots.
• Stem is eusteltic. Vascular bundles are conjoint, collateral, open and endarch.
• Secondary growth takes place.
• Wood may be monoxylic or polyxylic.
• Vessels and companion cells also occur in some gymnosperms (Gnetales) like
angiosperms.
• Heterosporous and have reduced gametophytes.
• Nucellus is surrounded by integument to form a structure called ovule.
• Like gymnosperms many angiosperms are wind pollinated.
 • Megaspore permanently remains inside the megasporangium and develops into female
gametophyte.
• Pollen grains grow into pollen tube.
• Male gametes are non-motile in majority of gymnosperms and angiosperms.
• Fertilization is siphonogamous.
• Suspensor is formed during development of embryo.
• Formation of endosperm.
• Formation of seeds from ovules.
• As in gymnosperms, polyembryony is found in several angiosperms.
• Embryogeny is endoscopic.
• Life cycle is similar in both groups

Difference between Gymnosperms and Angiosperms

GYMNOSPERMS ANGIOSPERMS
Plants are mostly woody trees. Plants may be herbs, shrubs or trees.
Companion cells in phloem are absent. Companion cells in phloem are present
Unisexual Bisexual as well as unisexual.
They are mostly perennial. May be annual, biennial or perennial
Rarely reproduce by vegetative means. Vegetative reproduction is very common.
Vessels in xylem element Present.
Cones are present.are absent. Absent.
Beautifying devices like sepals and petals Flowers consist of sepals and petals.
Pollination is anemophilous. May be anemo, entomo, hydro or zoophilous.
Ovules are naked. Ovules are enclosed within the ovary wall.
Presence of prothallius. Absent.
Archegonia present. Absent.
Endosperm is formed before fertilization. Formed after fertilization.
Endosperm is haploid. Endosperm is triploid.
Double fertilization absent. Present.
Cleavage polyembryony prevalent. Absent.
Zygote undergoes free nuclear divisions. Zygote does not undergo nuclear divisions.
Fruit formation absent. Present.

7. ECONOMIC IMPORTANCE OF GYMNOSPERMS:

1. Ornamental value: A number of gymnosperms are grown as ornamental plants, e.g.,

Cycas, Araucaria, Thuja etc.
2. Food Value:
• Sago starch obtained from pith and cortex of stem of C. revoluta, C. rumphi etc.
• Seed starch obtained from seeds of Cycas rumphii, Dioon edule etc. It is prepared into
flour and cooked before eating.
• Seeds of Pinus gerardiana (chilgoza) are edible.
• Kaffir bread prepared from the stem pith of Encephalartos.
• Young leaves of Cycas cooked as vegetables.
3. Medicinal value
• Ephedrine (alkaloid) extracted from Ephedra used in treating asthma, cough, cold,
bronchitis etc.
• Tincture of Ephedra is a cardiac stimulant.
• The juice extracted from young leaves of Cycas revoluta is used for curing blood vomiting
and flatulence.
4. Industrial Use
• Gum-Cycas gum used as adhesive, antidote for snake bites and using malignant ulcers.
• Tannins – Tannins extracted from bark of Araucaria, Pinus, Sequoia etc. used in leather
industry.
• Canada balsam – It is turpentine obtained from Abies balsamea and used as a mounting
medium in biological preparations.
• Amber (fossil resin) – obtained from Pinus succinifera. Wood of Pinus is used for
doors, poles, beams, railway wagon flooring etc.
• Plywood prepared from Podocarpus. Needles of Pinus and other conifers are used in
making fibre boards that are used in making packing cases.
 • Papers like newsprints, writing and printing papers are being prepared from the wood
pulp of Pinus, Picea,Abeis, Gnetum etc.
• The leaves of cycads are used for preparing baskets, mats, hats, brooms etc.
• The fibres obtained from the leaves of Cycas and Macrozamia are used for stuffing
pillows and making mattresses.
• Gymnosperms possess softwood used in preparation of light furniture, plywood,
packing cases, match sticks, railway sleepers, etc.
• Saw dust is employed in making linoleum and plastics.
5. Source of oils
• Oils extracted from seeds of C. revoluta, Macrozamia reidlei, Pinus cembra and
Cephalotaxus drupacea are used as edible oils.
• Red cedar wood oil extracted from the heart wood of Juniperus virginiana is used for
cleaning microscopic preparations and for oil immersion lenses.
• Oils obtained from Cedrus deodara, Ciyptomeria japonica and Cupressus
semperivirens are used in preparations of perfumes.

NOTE: Diagrams and illustrations are provided separately in the power

point.