Ferns are an important group of plants and they can be found growing in most places of the world, from temperate to tropical areas, in full sun or heavily shaded spots. They usually prefer a wet environment but can also be found in drier areas like Australia and Mexico where grow what are called "resurrection ferns." Those members of genera such as Cheilanthes, Paraceterach, Doryopteris and Selaginella will dry up and look dead during dry spells but will come back to life after rain. Of course the tropics with their constant humidity will host the greatest diversity of species. Ferns are botanically classed as Pteridophyta as they do not produce flowers and have a quite obscure propagation system. Pteridophytas (sometimes referred to as ‘inferior plants' while flowering plants are ‘superior plants' also include algae, mosses and liverworts but ferns differ because they have a vascular system (they are vascular cryptogams). Ferns number approximately 10,400 species classified in 240 genera but chances are there are many more. Throught history, they have been neglected by botanists who often concentrated on showier plants. The tropics have the greatest diversity, but also suffer of deforestation at an alarming rate and species that are unknown may very well remain so because of the disappearance of their natural environment. Most grow in the ground but in the tropics there are many epiphytes (growing on trees) and some lithophytes (growing on rocks); some ferns are climbers and there are even aquatic ferns which float freely on water (Salvinia spp. are used by fish amateurs as a refuge for the young) or send roots down in the mud like water lilies.
Ferns have probably been neglected because they do not have the same economical interest than flowering plants. Although some are edible they still have not made it to chef's table or the local supermarket. Nonetheless some 30 species are known to be used as greens, the fronds are edible, especially when they are still in a young stage known as croziers, used either raw but more often cooked. Some species are used as a starch supply and they are most often found in the large trunks of tree ferns that grow in India, Madagascar, New Guinea, Australia and the Philippines. Rhizomes can also be ingested and have been an important supply for Aborigines of Australia. Refreshing herbal tea can be made with the fronds of Dryopteris fragrans and Pellaea mucronata while if you run short of hop to brew your favourite beer you can use Pteridium esculentum as replacement. There are also many ferns used as medicinal plants and can help to cure many disorders ranging from parasitic worms to rheumatism, bowel disorders, bruises, bites, haemorrhages and so on. The aquatic ferns of Azolla genus are put to use as a fertilizer in rice paddies as they are host to an alga that can fix nitrogen from the air. But the most obvious use for ferns is probably the ornamental one, from nice potted Adiantum or Platycerium to the use of various species in bouquets.
As we cannot possibly go through the 10,400 different species today we will stick to a few species growing wild on Reunion. There are about 250 recorded species of ferns on the island, out of which some 18 are endemic strictly to Reunion while another 25 are endemic to the Mascareignes and will therefore be found also on the sister island of Mauritius.
We will start with a rather common species, Phlebodium aureum which is an exotic one as it comes from tropical zones of America. It is grown as both an ornamental and found in the wild in many locations; the ‘rabbit-foot fern' is very prone to variation and will therefore display a large variety of fronds shape, colour and size. It has large erect, light green fronds and a creeping rhizome covered with red-brown hairy scales resembling hairs, and can be easily propagated by rhizome cuttings. If we get close to a shady rock where water drips, we are sure to find the very delicate Adiantum. This genus, known as the maidenhair fern, is probably the most widely grown for ornamental use. There are a great many species, some with very delicately dissected fronds and they come from South America, Australia, Africa, Asia. Since they have been grown and enjoyed for a long time there are of course a large number of hybrids and cultivars. Young leaves are often brightly coloured from pink to bronze which add another element to play with. Growing as an epiphyte and almost covering the trunk, a nice staghorn originating from nearby Madagascar, Platycerium alcicorne displays large tough leathery fronds and is a common sight in wet forests. Another epiphytic species growing a few meters away is Vittaria isoetifolia with wiry fronds up to 60cm (2 feet) long. Looking like a weed, it can be found on trees as well as on rocks, in shady humid areas. The next one grows madly all over the place, even scrambling trees: Dicranopteris linearis is a very widespread plant which grows in light patches and forest edges, therefore invasive in cleared areas. It is so variable that it has 13 different varieties. Deeper in the forest, in moist and shady parts we encounter two primitive ferns; they are called primitive because they are extremely old and have some primitive aspects regarding their propagation system. Angiopteris evecta comes from Malaysia, New Guinea and Australia, it is a massive plant with large fronds and a fleshy trunk and enjoys growing by streams or creeks. The other one is Marattia fraxinea know locally as ‘fougère-tortue' (tortoise fern), an apt name as the remaining leaf basis looks like large tortoise scales. The erect rhizome can reach 30cm (1 foot) wide and the plant will commonly grow to two meters (6 feet) high, usually bearing only one or two leaves at a time. Of course, no way to leave before meeting our endemic tree ferns, all of which belong the Cyathea genus. Two of them, Cyathea borbonica and Cyathea excelsa, grow on Reunion and on Mauritius, in rain forests at low and medium altitude. Cyathea glauca is only found on Reunion and at high elevation in cloud forests. All three will produce a trunk, known as a stipe, which can reach 10 or even 15 meters (30 to 45 feet) high depending on the species! This stipe has been used for ages to make pots for orchids and is topped by a crown of large leaves arching somewhat like palms.
Well, this will be all we have time to discuss today, I know many people complain that ferns lack interesting colour and are not as rewarding to grow as orchids or bromeliads but they do have a strong presence in the tropics and always give a natural touch to gardens. They should be grown and enjoyed much more.