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Gymnosperms


The gymnosperms (from the Greek Gymnos: 'nu'; and sperma: 'seed') are terrestrial plants that live preferably in cold or temperate climate environments. This group includes plants such as Pine trees, at redwoods and the cypress trees.

Gymnosperms have roots, stem and leaves. They also have reproductive branches with modified leaves called strobiles. In many gymnosperms, such as pines and sequoias, strobiles are well developed and known as cones - which gives them the classification in the group of conifers.

There is seed production: they originate in female strobiles. However, gymnosperms do not produce fruit. Your seeds are "bare", that is, they are not enclosed in fruits.

Reproduction of gymnosperms

Let's use the parana pine tree (Araucaria angustifolia) as a model for explaining gymnosperm reproduction. In this plant the sexes are separated: the one with male strobiles does not have female strobiles and vice versa. In other gymnosperms, both types of strobilus may occur in the same plant.

The male strobile produces small spores called pollen grains. Female strobilus produces structures called eggs. Inside a mature egg comes a large spore.

When a male strobile opens and releases large amounts of pollen grains, these grains spread in the environment and can be blown to the female strobile. Then a pollen grain can form a kind of tube, the pollen tube, where the sperm nucleus, the male gamete, originates. The pollen tube grows until it reaches the egg, into which it introduces the sperm nucleus.

Inside the egg, the large spore it houses develops into a structure that guards the oosphere, the female gamete. Once inside the egg, the sperm nucleus fertilizes the oosphere, forming the zygote.


Cones or strobiles

This, in turn, develops into an embryo. As the embryo forms, the egg becomes a seed, a structure that contains and protects the embryo.

In pines, the seeds are called pine nuts. Once the pine nuts are formed, the female cone is called pine cone. If scattered in the wild by some spreading agent, the seeds can germinate. When germinating, each seed gives rise to a new plant.

The seed can be understood as a kind of "biological fortress" that shelters and protects the embryo against dehydration, heat, cold and the action of certain parasites. In addition, the seeds store nutrient reserves, which feed the embryo and ensure its development until the first leaves are formed. From there, the new plant manufactures its own food through photosynthesis.


The pine cone and Araucaria seed