Ferns are some of the oldest plants on Earth and grew in vast forests dating back to the primary era.
They dominated the flora of the Carboniferous age (late primary era), some 350 million years ago. They therefore existed long before dinosaurs and flowering plants (150 million years ago). Some ferns from that time still exist, such as the royal fern, whose fossils have been found in rocks dated 200 million years old.
There are over 12,000 species of ferns whose genealogy goes back hundreds of millions of years, whereas it is rare to find fossils of animal species that are still living today. In plant evolution, ferns were the first plants to have had a vascular system.
Ferns are plants without flowers or seeds (cryptogams) as are algae, fungi, mosses or lichens.
They are classified into several families: Polypodiaceae, Aspleniaceae, Athyriaceae, Pteridaceae, Dryopteridaceae, etc. Ferns are extremely adaptable and can grow anywhere except in the polar regions. Ten thousand species have been recorded of which three-quarters grow in the tropics. There are some 1,500 species in the temperate regions.
Frond = rachis = frond rib
Sori = clusters of round or elongated, brown or white sporangia, on the underside of what are known as fertile fronds.
Sporangia = spherical structures with an annulus or ring, inside which the spores are formed and which thus enable the ferns to reproduce.
Spores = are neither male nor female, they are scattered by the wind, and germinate in a damp environment to produce the prothallus on which the sexual organs develop.
Prothallus = this is a green 5-6 mm, heart-shaped leaf, fixed to the ground by hair roots. As the prothallus matures the antheridium (male organ) ,which contains antherozoids (sperm cells), forms on its edge. The archegonium (female organ), which produces the egg cell (oosphere), forms at the centre of the prothallus.
Cyrtomium falcatum - Step, E., Bois
Favourite flowers of garden and greenhouse, vol. 4: t.305 (1896-1897)
A few reminders about cells: every living organism is composed of cells. Male and female cells with n chromosomes cells are formed in the sexual organs of living organisms. The cells of a living organism created by the fertilization of these cells with n chromosomes will therefore have 2n chromosomes.
Chromosomes carry the genetic characteristics of every living organism.
1) When mature, the sporangia (2n chromosomes) grouped in sori open up and release copious amounts of minute, dust-like spores.
2) in a damp environment, the spores (2n chromosomes) germinate into a heart-shaped prothallus, a few millimetres long, which is attached to the ground by hair roots. It has a single layer of cells with 2n chromosomes.
3) On the tip of the prothallus develop the antheridia which will produce antherozoids, male cells with n chromosomes and the archegonia which will produce an egg cell or oosphere, female cells with n chromosomes. So the prothallus is therefore where the reduction of chromosome number takes place.
4) The flagellated antherozoids or sperm cells swim to the archegonia, attracted by their mucilage. Only one sperm cell reaches the egg cell and fertilises it to give birth to the first cell with 2n chromosomes of a new fern.
5) The new fern develops on the prothallus which gradually disappears.
Sowing spores: difficult to achieve in the garden although nature does it easily. Dividing stems and rhizomes: preferably in the early spring, same method as for perennials. Planted in a soil mixed with very wet compost. Water frequently.
Ferns are elegant, rarely ill, have few pests apart from slugs on some species, are hardy, grow in difficult places (banks, old walls, at the feet of conifers, etc.,) and as such are really foolproof garden plants.
So gardeners really ought to think about planting them more often. In addition, they have a lifespan from 35 to 100 years.
When? In the spring or autumn
# ideal soil: light, damp, well-drained, humus-rich and lightly acidic. If the soil is too heavy, add some drainage elements (sand 5 mm). You can also put some compost, soil and dead leaves in the planting hole. NO CHEMICAL FERTILISERS
# location: shade, partial shade, no direct sunlight for most species. Cool soil will help ferns grow in a sunnier location.
Avoid windy sites as the fronds of some ferns are fragile and break easily.
Plant the fern to a shallow depth. The rhizome should be flush with the ground to prevent rotting. Pot cultivation: for ferns which are less than 60 cm and with rhizomes that don't need to spread, plant them in containers that are wider than they are tall; choose pots that suit the size of the fern.
Beware of ferns drying out, even in the winter. Add slow-release organic fertiliser in the spring, but divide by 2 the amounts indicated.
Mulching with their dried fronds and leaves is worthwhile for two reasons: it helps retain moisture and also enriches the soil with humus to feed the plant. Water in dry weather. Protect with mulch during particularly cold spells. And the best thing: leave the dead leaves where they are and remove the dried fronds in the springtime.
The foliage of most ferns grows back in the springtime. As the fronds get damaged during the winter, they should be cut back at the beginning of spring before the new fronds appear.
Athyrium filix-femina - Prof. Dr. Otto Wilhelm Thomé
Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany
In a rockery, on an old moss-covered wall, on an embankment, underneath hedges, deciduous trees or conifers. In pots, on a shady terrace.
Ferns are trouble-free, easy to grow plants, which are attractive because of their elegant shapes. They give structure to perennial beds and add interest to semi-shaded rock gardens.
Ferns can have an upright or bushy habit and whether they have evergreen, semi-evergreen or deciduous fronds, whether they change colour depending on the season and whether they have simple or cut-out shaped fronds and whether they're 4-5 cm or over 1 metre tall, they always fit into a garden.
The adaptability of ferns enables them to grow in very different environments. For example, Polypodium vulgare grows equally well on an embankment, in the shade of a deciduous tree, on an old tree trunk or on top of a sunny wall; the size of fronds varies according to the situation.