Gymnosperm is a large class that includes a number of fossils and living forms (Fig. 9.1).
Various attempts have been made by different works to classify the gymnosperms.
The classification as proposed by C.J. Chamberlain (1935) is as follows:
(i) Cycadales include 11 living genera and more than 100 species of cycads.
(ii) Cycads resembles with the pteridophytes.
(iii) The members are woody sporophytes which appear palm-like.
(iv) All are dioecious,
(v) Young leaves show circinate vernation.
Examples: Cycas, Microcycas, Zamia pygmaea (smallest gymnosperm), Chigua, Stangeria etc.
(i) Ginkgoales include only one living member i.e. Ginkgo biloba (Maiden hair tree) and is the oldest living seed plants persisted with little change till now.
(ii) Leaves are leathery, fan- shaped and deciduous
(iii) Male strobili catkin-like,
(iv) Wood pycnoxylic.
(v) Ovules arise in groups (2-10).
(vi) Endosperm has beak like protuberance called tent pole.
(i) It is the largest order of living gymnosperm.
(ii) All members are perennial with ex-current (conical) appearance,
(iii) Leaves dimorphic i.e. foliage and scale leaves present,
(iv) Wood is pycnoxylic.
(v) Pollens and seeds are winged,
(vi) They are dominant forest-makers in the colder region of earth due to – xerophytic nature, evergreen nature, presence of mycorrhizas, scale leaves, resins to plug injury, enzymes activity even at – 35° C.
Pinus, Sequoiea (Red wood tree, the largest gymnosperm, 366 ft.), Taxodium,Juniperus, Saxegothea, Araucaria (commonly called Monkey Puzzle)
(i) A small but highly evolved group of gymnosperms represented by 3 genera i.e. Ephedra, Gnetum and Welwitschia.
(ii) They are the ancestors of Angiosperms (flowering plants),
(iii) Unlike other members, gnetales have vessels in xylem.
(iv) Flowers arranged in compound strobili or inflorescence,
(v) Embryo with 2 Cotyledons.
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:
i. ‘Sago’ starch obtained from pith and cortex of stem of C. revolute, C. rumphi etc.
ii. ‘Seed starch’ obtained from seeds of Cycas rumphii, Dioon edule etc. It is prepared into flour and cooked before eating.
iii. Seeds of Pinus gerardiana (chilgoza) are edible.
iv. ‘Kaffir bread’ prepared from the stem pith of Encephalartos.
v. Young leaves of Cycas cooked as vegetables.
3. Medicinal value:
i. Ephedrine (alkaloid) extracted from Ephedra used in treating asthma, cough, cold, bronchitis etc.
ii. Tincture of Ephedra is a cardiac stimulant.
iii. The juice extracted from young leaves of Cycas revoluta is used for curing blood vomiting and flatulence.
4. Industrial Use:
i. Gum-Cycas gum used as adhesive, antidote for snake bites and using malignant ulcers.
ii. Tannins – Tannins extracted from bark of Araucaria, Pinus, Sequoia etc. used in leather industry.
iii. Canada balsam – It is turpentine obtained from Abies balsamea and used as a mounting medium in biological preparations.
iv. Amber (fossil resin) – obtained from Pinus succinifera. Wood of Pinus is used for doors, poles, beams, railway wagon flooring etc.
v. Plywood prepared from Podocarpus.
vi. Papers like newsprints, writing and printing papers are being prepared from the wood pulp of Pinus, Picea,Abeis, Gnetum etc.
vii. The leaves of cycads are used for preparing baskets, mats, hats, brooms etc.
viii. The fibres obtained from the leaves of Cycas and Macrozamia are used for stuffing pillows and making mattresses.
5. Source of oils:
i. Oils extracted from seeds of C. revoluta, Macrozamia reidlei, Pinus cembra and Cephalotaxus drupacea are used as edible oils.
ii. Red cedar wood oil extracted from the heart wood of Juniperus virginiana is used for cleaning microscopic preparations and for oil immersion lenses.
iii. Oils obtained from Cedrus deodara, Ciyptomeria japonica and Cupressus serm-perivirens are used in preparations of perfumes.