Fern Facts
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Living Fossils
Ferns have an ancient history, with fossils of ferns and their spores dating back hundreds of millions of years. But today’s ferns are far from primitive: they are a diverse and successful group of plants that continues to evolve. Their fossils offer insights into evolution.
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Spores
Ferns reproduce by spores rather than flowers and seeds. These tiny spores are usually produced in structures on the fronds and can grow into new plants through a fascinating life cycle, very different from that of seed-producing plants and remarkably successful today.
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Adaptable
Ferns grow in an extraordinary range of habitats, from wetlands and damp pastures to monsoon forests, cloud forests, deserts, trees and cliffs — some even grow in water. Understanding these different habitats can help us provide the conditions they need to thrive in cultivation.
A fossil fern.
An ancient and diverse group of plants
Ferns are vascular plants that reproduce by spores rather than seeds. Like seed plants, they have true roots and a vascular system that transports water and nutrients through the plant. Their leaves, known as fronds, carry out photosynthesis and, in most ferns, also play a role in reproduction.
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Although ferns have an evolutionary history stretching back hundreds of millions of years, it is wrong to think of the ferns we see today as unchanged survivors from a prehistoric world. Ferns have continued to evolve, diversify and adapt. There are over 13,000 species, probably closer to 15,000, adapted to an extraordinary range of environments around the world.
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Their ability to disperse by spores also allows some ferns to colonise newly exposed or disturbed ground remarkably effectively. Ferns have played this pioneering role throughout their long evolutionary history and continue to do so today.
Fern croziers.
The unfurling frond
One of the most recognisable features of a fern is the way a new frond develops. Young fronds are typically tightly curled into a crozier, gradually unfurling as they grow. The main frond and its individual divisions, or pinnae, may both show this characteristic coiling.
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It is one of the pleasures of growing ferns: a tightly curled crozier can develop surprisingly quickly into an intricate new frond.
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Ferns in the wild
Ferns occupy an extraordinary range of habitats. They can be found in forests and damp grasslands, on trees and rocks, in seasonally flooded areas and even in water. Although we often associate them with cool, shady and damp conditions, some species are adapted to much drier environments.
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Our idea of a typical fern is often influenced by where we live. In northern Europe, for example, we are most familiar with terrestrial ferns growing on the ground, while in tropical regions many of the most striking ferns grow as epiphytes on trees or as lithophytes on rocks.
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This diversity is particularly important when growing ferns. Some tropical species are quite happy in ordinary household conditions, while others need carefully managed light, temperature, humidity and growing media. Understanding where a fern comes from can provide valuable clues to the conditions it needs in cultivation.
Fern sori.
Ferns and their allies
You may sometimes come across the term fern allies. These are ancient vascular plants that, like ferns, reproduce by spores rather than seeds and share many similarities in their life cycles. They include clubmosses such as Lycopodium, spikemosses (Selaginella) and quillworts (Isoetes).
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Although they are not true ferns, fern allies have long been studied and grown alongside them. They are an important part of pteridology — the study of ferns and their allies — and range from tiny creeping plants to aquatic, terrestrial and epiphytic species found in habitats around the world.
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You may also encounter the term cryptogam. This is a much broader, traditional term for organisms that reproduce without flowers or seeds. As well as ferns and their allies, it has been used for groups such as mosses, liverworts, algae and fungi. It is not a single evolutionary group, but the term is still encountered in botanical literature and collections.
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Understanding fern terminology
Ferns have their own vocabulary, and knowing a few of the most commonly used terms makes identifying and describing them much easier.
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The main stem of a fern is the rhizome. Depending on the species, this may grow upright or creep across the ground, rocks or trees. The fronds arise from the rhizome.
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A fern growing on the ground is described as terrestrial. One growing on another plant, without taking nutrients from it, is epiphytic, while a fern growing on rocks may be described as lithophytic.
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Fronds are often divided into smaller sections called pinnae, which may themselves be divided into pinnules. The stalk between the rhizome and the leafy part of the frond is the stipe; where it continues through the blade it becomes the rachis.
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The surfaces of the rhizome and fronds can also provide useful clues for identification. They may be smooth (glabrous) or covered with hairs or scales. You may encounter more precise terms such as pubescent, hirsute or villous to describe different types of hair. Collectively, these surface coverings may be referred to as the indumentum.
Specialised fronds adapted for carrying large numbers of spores.
Fern gametophytes and a few small sporophytes.
Sori and spores
Spores are produced inside tiny structures called sporangia, which are usually grouped together in clusters called sori. The individual sporangia are minute, but can just be seen with the naked eye.
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Sori are commonly found on the underside or margins of fertile fronds, although their position and form vary widely between different groups of ferns. In some ferns they are protected by a thin covering called an indusium. Its shape and the way it is attached can be useful for identification: some are attached centrally and open rather like tiny umbrellas, while others are attached along one side.
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Other ferns have uncovered, or naked, sori, while some produce specialised fertile fronds adapted to carry large numbers of spores. When mature and conditions are suitable, the spores are released from the sporangia and may be carried considerable distances.
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The fern life cycle
The fern life cycle is quite different from that of a flowering plant. The familiar fern plant is the sporophyte. It usually produces haploid spores, each carrying a single set of chromosomes, which are released from the sporangia and may be dispersed by wind.
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If a spore reaches suitable damp conditions, it can grow into a small gametophyte, also known as a prothallus. This bears the reproductive structures: the male antheridia and female archegonia.
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Water is essential for fertilisation. Motile sperm released by the antheridia swim through a film of moisture to reach an egg in an archegonium. After fertilisation, a new diploid sporophyte begins to develop and eventually becomes the fern plant we recognise.
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This cycle between the haploid gametophyte and diploid sporophyte stages is known as the alternation of generations.