Gymnosperms

Gymnosperms are called so because they have naked seeds. Therefore, they are superior to Pteridophytes because they are seed-bearing plants. They are inferior to Angiosperms or Flowering plants because their ovules are in an unenclosed condition means naked. In the flowering plants or Angiosperms, the ovules are covered. The plants in this group are the conifers, cycads, Ginkgo, and Gnetales. Since both angiosperms and gymnosperms have seeds, both of them are placed in Spermatophytes.

Salient Features

• Generally, Gymnosperms are woody trees, shrubs and climbers. Many of them are xerophytes as they can survive where there is no water such as deserts.
• Gymnosperms have tap roots. Tap roots are somewhat straight to tapering plant root that grows vertically downward. It forms a center from which other roots sprout laterally. One common example of Tap root in Angiosperms is Carrot. Please note that plants which have tap roots are difficult to relocate or transplant.
• The roots of many Gymnosperms have symbiotic relations with algae or fungi (mycorrhiza). For example, the roots of Pinus have mycorrhizal relations with a fungus.
• The stem is erect and similar to advanced plants. It may or may not be branched. Leaves are either green or brown. The Xylem has bordered pits BUT there are NO vessels. Vessels in Xylem are found in ONLY Angiosperms. There are no companion cells in Phloem. Companion cells in Phloem is found in ONLY Angiosperms.

Life Cycle

The dominant phase of life is Sporophyte as in all other vascular plants. The gametophyte is relatively short-lived. Two spore types, microspores and megaspores, are, in general, produced in pollen cones or ovulate cones, respectively, which can be called male cones and female cones. Male cone is small and short-lived. Female cone is large and long-lived. A short-lived multicellular haploid, gamete-bearing phase (gametophyte) develops inside the spore wall. Pollen grains (microgametophytes) mature from microspores, and ultimately produce sperm cells; megagametophyte tissue develops in the megaspore of each ovule, and produces multiple egg cells. Thus, megaspores are enclosed in ovules (unfertilized seeds) and give rise to megagametophytes and ultimately to egg cells. During pollination, pollen grains are physically transferred between plants, from pollen cone to the ovule, being transferred by wind or insects. Whole grains enter each ovule through a microscopic gap in the ovule coat (integument) called the micropyle. The pollen grains mature further inside the ovule and produce sperm cells.

Two main modes of fertilization are found in gymnosperms. Cycads and Ginkgo have motile sperm that swim directly to the egg inside the ovule, whereas conifers and gnetophytes have sperm with no flagella that are conveyed to the egg along a pollen tube. After fertilization (joining of the sperm and egg cell), the zygote develops into an embryo (young Sporophyte). More than one embryo is usually initiated in each gymnosperm seed. Competition between the embryos for nutritional resources within polyembryonic seeds produces programmed cell death to all but one embryo. The mature seed comprises the embryo and the remains of the female gametophyte, which serves as a food supply, and the seed coat (integument).

What are economically Important Gymnosperms?

• Coast Redwood of California, which we know as the tallest plant / trees of the world are Gymnosperms. Its botanical name is Sequoia sempervirens spp. gignatica. The height is 420 fits and they are long living plants can live up to 1200-1800 years. The plant is an important timber.
• Many Gymnosperms are called the “living fossils”. This is because many of them represent the one of the few, if not the only, surviving members of a taxonomic group, with no close living relatives. Well known example of a living fossils are Cycas and Ginkgo Biloba, a tree which is literally in a class by itself. Like many other living fossils, Ginkgo is also remarkably similar anatomically to older relatives in the fossil record.
• Canada balsam is obtained from Abies balsamea, a Gymnosperm. This is the resin of the plant, very sticky, colorless and odorless. It has high optical quality and was used once upon a time in making the invisible-when-dry glue for glass. Similarly, it was used as a glue for prisms. Today it is used to fix the scratches in the glasses and also in cough syrups.
• Ephedrine, which is used in Medicines as stimulant, appetite suppressant, concentration aid, decongestant, and to treat hypotension associated with anaesthesia, is obtained from Ephedra distachya, which is also a Gymnosperm. It has been used in the treatment of asthma and bronchitis for centuries. Please note that Ephedra is a naturally growing Gymnosperm in Rajasthan.
• Sago is a major staple food for the lowland peoples of New Guinea and the Moluccas. It is traditionally cooked and eaten in various forms, such as rolled into balls, mixed with boiling water to form a paste, or as a pancake. Sago is often produced commercially in the form of “pearls”. Sago pearls can be boiled with water or milk and sugar to make a sweet sago pudding. It is obtained from Cycas revoluta and Please note that Sabudana, which is used as a staple food in India, particularly in Hindu rituals and Vratas is NOT obtained by Cycas BUT is obtained from tapioca roots which is an Angiosperm of family Euphorbiacae.
• Chilgoza is obtained from Pinus gerardiana, known as the Chilgoza Pine. Chilgoza is one of the most important cash crops of tribal people residing in the Kinnaur district of Himachal Pradesh, which seems to be the only place in India where Chilgoza pines are found.
• Cedar wood is obtained from many species of the Gymnosperms. Similarly Chir wood is obtained from Chir Pine or Pinus longifolia. The Pinus species of Gymnosperms contain the “winged pollen grains”. Pinus aristata is oldest living Gymnosperm.