Tag: gymnosperms

Conifers are a magnificent group of gymnosperm plants that produce seeds without fruit or flowers. They include some incredible trees, such as the 'Giant Sequoias' of North America, that can grow over 110 m tall.

The conifers are by far the largest group of gymnosperms with around 630 species worldwide of a total approximation of around 860 species. The word 'conifer' is Latin for 'cone bearing', because conifers produce cones within which they produce pollen (male cone) and grow seeds (female cone).

Conifers are all woody plants, mostly trees and a few shrubby species, they have either needle-like or scale-like leaves and most species are evergreen. They include the economically important pines and many other timber species that are exploited for use in construction and paper.

Gymnosperms have archegonia but no antheridia. The plants of this division are heterosporous. While the microspores or pollen grains produce the male gametophyte, the single megaspore within megasporangium (nucellus) develops into a female gametophyte, that bears two or more archegonia or female sex-organs. Also, there is no antheridium in which the sperm are produced.

• Ferns, algae, and bryophytes find water as an essential element for fertilisation to take place. Because they are in need of water for the movement of sperms, etc. Whereas the condition is not similar in the case of Cycas.

Fertilization in Cycas;

• The pollen tube grows towards the archegonium of the female gametophyte. There, the end of the pollen tube bursts and discharges its contents into the archegonia chamber.
• The spermatozoids are set free in the archegonia chamber. They swim towards the neck of the archegonium and make their way down to the egg cell. One of the spermatozoids fuses with the egg uncles i.e. oosphere.

Fertilization is thus effected. 

Casuarina is a xerophyte whereas Pistia, Hydrilla and Vallisneria are hydrophytes.

Gymnosperms are those seed plants in which the seeds remain exposed over the surface of the megasporophylls because the latter are not folded to form pistils and thus lack ovary. Flowers are absent and thus fruits are not formed.

Gymnosperms, example. Cycas, Pinus, Cedrus etc, bear reproductive structures in the form of cones. The cones that bear female reproductive structures are called female cones. Each female cone contains spirally arranged megasporophylls, that have ovules directly attached to them,  that is,ovules not enclosed in the ovary or are naked. After fertilization the ovule forms the seed and the ovary forms the fruit. Since, in gymnosperms ovary is  absent fruits are not formed.