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Introduction to
Gymnosperms
The 'Gymnosperms', are the
most ancient seed plants that originated during the late 'Palaezoic era', that flourished well
during the 'Mesozoic'. The word 'gymnosperm' was used in 300 BC. by Theophrastes, a pupil of
Aristotle in his book "Enquiry into Plants". The term Gymnosperm (Gymno = naked;
sperm = seeds) means plants whose seeds are naked (or) unprotected by the seed coat. The
Gymnosperms are characterised by freely exposed ovules before and after fertilisation.
The plants are 'Sporophyte', to adapt to
the various environmental conditions, and widely distributed through out the world.
Gymnosperms includes both living and fossil plants. The modern gymnosperms are commonly
grouped under four orders namely 'Cycadales', the 'Ginkgoales', the 'Coniferales' and the
'Gnetales'. Cycadales and the ginkgoales includes living members that have a long fossil
history and can be regarded as "living fossils".
Gymnosperms are economically most
important; about 80 % of timber comes from conifers and various substances such as turpentine
and resins, which are ingredients in varnishes and certain plastics. Because of their
attractive appearance, conifers are grown commercially. Amber, the fossilised resin of
prehistoric conifers, is often cut and polished to make jewellery.
The living fossil 'Ginkgo biloba', 'Cycas cone', 'Pinus cone' and 'Gnetum'
species are exhibited in the Systematic Botany Gallery.
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Cycas circinalis
Fern Palm
Male cone:- It is a 'Gymnosperm' plant,
belonging to the family 'Cycadales'. Male cone of this species are borne singly and terminally
on the main stem. The male cone is woody in texture. It is a compact long spindle-shaped and
blunt-ended. It consists of central woody axis bearing 'microsporophylls' (stamens) in a close
and compact (close fittings) spiral. Each microsporophyll is a woody flattened wedge-shaped
structure consisting of a narrow lower portion broadened into a flat sterile disc above. It
bears several hundred 'microsporangia' which are arranged in clusters, called 'sorus'. It
produces a large number of 'microspores' (pollengrains). The male cone is exhibited in the
Systematic Botany Gallery.
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Cones The plant
belongs to the division 'Gymnosperms', class 'coniferals'. Pines are tall, graceful, evergreen
trees. The tree has a typical pyramidal shape because the lateral branches are almost
horizontal and their length gradually decreases from below upwards. In India, pines are
largely distributed in the Himalayas and Western Ghats. The tree represents a 'sporophyte'.
Pines are monoecious, which means that
the male and female reproductive structures, known as 'cones', occur on different branches of
the same tree. Male cones arise in clusters in place of dwarf shoots. Each cone consists of
numerous microsporophyll, arranged spirally on the central axis. Female cones are borne at the
tips of long shoots and generally occur in pairs.
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Ginkgo biloba
Maiden hair tree
It is a deciduous
'Gymnosperm' tree, belonging to the family 'Gneataceae', with long-stalked, fan-shaped leaves
more or less indented with dichotomous veins, thus resembling the leaflets of the Maiden hair
fern, hence it is called 'Maiden hair tree'. It is a living fossil.
The distribution is known only in
cultivation in China and Japan whence it has been introduced elsewhere. This plant is kept as
herbarium under the Systematic Botany Gallery.
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Next Gallery
Systematic Botany