14 DAY TRIAL // 1.The first ferns appeared 350 million years ago. They form a plant group called Pteridophyta. These are the first superior plants, having a cuticle impermeable to water, roots and an inner tissue specialized for transporting water and nutrients between the water absorbing organs (roots) and food producing ones (leaves), unlike mosses that got out of the water at the same time. These traits ensured the exit of the first ferns and their descendants in colonizing the ground.
2.Ancient ferns were 30 m (100 ft) tall, and while modern clubmosses (a fern group) are dwarf, the ancient ones were 15 m (50 ft) tall. They formed massive forests from which a lot of the carbon and petroleum we use today formed.
3.The stem of ferns vary from rhizomes (resembling those of the iris) to real stems, and even vine-like ones. Many tree ferns form right trunks the way palms do it, the remains of the dead leaves keeping stuck on the trunk and protecting the stem.
Ferns' roots grow directly from the stems (they are adventive), but resemble the roots of superior plants.
4.There are 10,000 living fern species, found all over the world. Even in the Arctic region there are 500 cold adapted species. About 500 species have scales and hairs that help them live in desert environments. Some are found at altitudes of 5,000 m (16,666 ft). As ferns flourish in wet conditions, the highest number is found in wet tropics.
5.Membranous ferns are so small, that a whole colony can grow under an average sized leaf of a tree. Their thin leaves are almost transparent and require high humidity for surviving. On the other side, there are about 700 tree fern species. In New Zealand and Australia they may be 15 m (50 ft) tall with leafs 6 m (20 ft) long.
Some ferns float on stagnant water, like water fern (Azolla and Salvinia), forming carpets on the surface of the ponds during the summer, and some can turn into a pest. Climbing ferns (Lygodium) are vines up to 10 m (33 ft) long.
6.Ferns do not have seeds, nor flowers. They produce spores, like algae, fungi or mosses, in capsules called sporangia. They are grouped in the lower side of the leafs, forming brown patterns. A fern can have thousands of sporangia. The capsules explodes when mature, spreading the spores through the wind. The spores germinate in shady, wet places, forming in a few months a small heart shaped plant, just 6 mm wide. This is a prothallus, a hermaphrodite individual carrying the sex organs of the fern: male antheridia with sperms and female archegonia with eggs. If a thin layer of water covers the prothallum, sperms can swim to eggs, fecundating them. The fecundated egg develop into an embryo forming the proper fern, and the prothallum dies. The prothallum lives till fecundation takes place, usually about 9 months.
7.Besides the common ferns, there are also clubmosses (Lycopodium, Selaginella, Stylites, Isoetes, Phylloglossum). Unlike common ferns, they form two types of spores: microspores generating male prothalli and macrospores generating female prothalli. Like in the case of the pollen of evolved plants, sperms are not released from the microspore.
8.Horsetails (Equisetum) too are a type of ferns. They exist for about 300 million years. The 25-30 species of horsetails have leafs reduced to scales. The articulated stems, hollow inside, make photosynthesis. Fertile stems ends in cones filled by sporangia. These ferns grow usually near water and their underground stems spread over large distances, making them difficult to combat. They vary from 15 cm (0.5 ft) to 1 m (3.3 ft) in height, but, hundreds of millions of years ago, there were huge tree species of horsetails (like Calamites). Unlike other ferns, horsetails are more abundant in cool, temperate areas. Some species are rich in silicon dioxide (the mineral glass is made of), that's why they were used for polishing ivory and metals.