What is the life cycle of ferns like?

Ferns (class Filicopsida) are vascular plants, that is, they have roots and conductive vessels for the xylem and phloem, but they have a life cycle very different from the rest of vascular plants (conifers and angiosperms).

One of the most outstanding characteristics of the life cycle of ferns is the alternation between generations of haploid individuals (with a single chromosome copy) and generations of diploid individuals (with two chromosome copies).

Ferns Overview

To understand how ferns reproduce, it may be helpful to first learn about the salient features of their anatomy.

Each leaf of the fern is called frond or frond and is considered a type of megaphyll or large leaf. The fronds are pinnate, meaning they consist of a central axis with leaflets to the sides.

On the anterior face of the leaflets appear the sorossome structures that group sporangia or organs forming spores. Not all fronds have sporangia, only fertile fronds.

Spores are tiny structures that contain the genetic material for a new fern to grow. The spores are formed inside the sporangia, which are sometimes protected by membranes called indusians and other times they are exposed directly to the air.

alternation of haploid and diploid generations

The life cycle of ferns requires two generations of plants to complete, each with a different genetic makeup. in one generation the genetic makeup is diploid and the other is haploid.

The fern leaves are part of the diploid generation, which means that each of the cells of the individual has two copies of chromosomes. This generation is known as sporophytebecause it is the one that produces spores.

When the spores germinate, they do not give rise to a new sporophyte, but instead give rise to a different individual in the form of a small seedling. This generation is known as gametophyteis haploid and instead of spores it produces gametes to reproduce.

life cycle steps

Starting with the sporophyte, which would be the fern as we normally recognize it, the life cycle follows the following stages:

  1. The diploid sporophyte produces haploid spores. to reproduce. Spores are produced by meiosisthe same type of cell division by which eggs and sperm are produced in animals and angiosperm plants.
  2. A gametophyte grows from a spore through mitosis. Unlike meiosis, mitosis maintains the number of chromosomes, so the gametophyte is haploidas well as the spore from which it came.
  3. The gametophyte produces gametes (eggs and sperm). It is noteworthy that These gametes are produced by mitosis., unlike the gametes of animals and angiosperms; meiosis reduces the number of chromosomes, from diploid to haploid, but here it is not necessary because the cells of the gametophyte are already haploid. In most fern species, the same gametophyte produces both eggs and sperm. Eggs are produced in structures called archegonia and sperm are produced in the antheridia.
  4. When water is present, the sperm uses its flagella to travel to and fertilize an egg.
  5. The fertilized egg remains attached to the gametophyte. When the genetic material of the sperm and the egg fuse, a diploid embryo is formed. The embryo develops by mitosis to again form a diploid sporophyte. completing the life cycle.

The clues in the life cycle is that the gametophyte and the sporophyte are genetically different. Also key is the ability of the gametophyte to reproduce by autogamy or self-fertilization (egg and sperm from the same individual), or by halogamy or cross-pollination.

The advantages of autogamy is that fewer spores are needed to complete the life cycle; Also, a genetic line adapted to its environment can reproduce and maintain its traits. Allogamy, when it occurs, increases the chances of genetic variability.

Other forms of reproduction of ferns

The life cycle of ferns in which sporophytes and gametophytes alternate occurs when they reproduce through sexual reproduction, but ferns also follow various forms of asexual reproduction:

  • apogamy: from a gametophyte a sporophyte develops without fertilization occurring. This method of reproduction occurs when environmental conditions are very dry.
  • rhizomes: the rhizomes can expand through the soil and new sporophytic ferns can sprout from them.
  • Vegetative reproduction or propagation: sporophytes are formed from specialized stems of an original sporophyte. When the sporophytes created in this way reach the ground and take root on their own, they can continue a life as an independent individual.
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