An Introduction to Tree Ferns

Tree ferns are becoming almost common in cultivation, especially in the U..K. and garden centres and nurseries sell thousands and thousands every year. Here Peter gives us some background to this and other species, and reminds us how little we really know about this by now familiar plant.
Peter Strong, Fernleigh Farm Nursery, Kloof, South Africa

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Above: 'Looking into the past'. Unidentified tree fern in Costa Rica.

Introduction

The journey into discovering tree ferns requires that we first come to know a little about ferns in general. The age of ferns is generally agreed to have been the Carboniferous Age, some 350 million years ago, when ferns dominated the planet's vegetation. Most of the ferns of that age became extinct, though some developed into the ferns that we know today. Strangely enough, flowering plants were not found in the dim distant eons. Ferns can really therefore be described as primeval, and, as such, they can be said to be among the oldest living things. Ferns are incredibly diverse and have intricate designs. Botanists agree that there are over 11,000 in 240 genera. They can be found in nearly any climate, from cold temperate to the hot, steamy tropics. The inclination of some ferns to spawn mutations provides an ever increasing number of "new" species on a regular basis, drawing the attention of the fern lover.

Structure

Ferns are considered to have more complicated structures than almost all other plants. Describing them therefore requires using terms that may sound strange to many. For instance, we do not talk about leaves; they are called fronds. These fronds have a stalk, called the "stipe," and a "blade," which is the leafy part of the frond. The size of fronds varies greatly, from the giant tree fern fronds of several meters in length to the tiny little mosquito fern which is only a few millimeters in length. Ferns have rhizomes, which are actually the stems of the plants, and they can be vertical or horizontal. From these rhizomes the fronds will emanate. They can be thick or thin. Some of the tree ferns have rhizomes that are approximately 75cm in diameter, and stand 12m tall. As stems, these rhizomes can be cut off at ground level and the top half can be planted, with every good chance of the top stem growing again.

Reproduction

The seeds of ferns, called "spore," come from the sporangia, which are minute pouches that produce the dust-like spores from which ferns are propagated. They are virtually invisible to the naked eye, and are produced by the million. In ancient times ferns were thought to be magical because no one could actually see the spore, and yet they grew. Folklore and mysticism of bygone ages ascribed magical properties to the humble fern. The strange little moonwort fern (Botrychium lunaria ) was supposed to have the power to open locks. This belief has figured prominently through the ages; even Shakespeare refers to the mysterious fern in Henry IV when Chamberlain says to Gadshill: "You are more beholding to the light than to fern seed for your walking invisible." This mystery was only unraveled in the 1800's.

Tree Ferns

The tree ferns we know today are small in comparison to their predecessors, which were infinitely taller and thicker stemmed. Not withstanding, there are still species today that stand over 15m tall with trunks of over 80cm diameter, and frond canopies of 10m or more. Recently some Dicksonia antarctica were found that were estimated to be over 500 years old and still growing. Sadly, with the ever increasing number of humans and their demands, these plants are in danger of becoming extinct, and all tree ferns are today covered by the CITES* convention.

Tree ferns are often mistakenly described as any ferns that have trunks. However, there are but two genera that make up the total family of these wonderful plants. There are others which form a trunk, but they are not true tree ferns. The two genuine genera that make up the tree fern family are Cyathea, of which there are some 800 species, and Dicksonia, of which there are only some 26 species. In general, they are tropical to sub-tropical, but several do tolerate much cooler climates. It has even been suggested that a member of the genus Cyathea may have the ability to protect itself from being killed by frost. Let me hastily add that this is being looked into and has not yet been proven. One of the fascinations with tree ferns is that every now and again some one, some where, finds a new plant or plant attributes that suggest that we know precious little about these plants, and have an awful lot more to learn.

It is generally accepted that many more tree ferns are found in the southern hemisphere than the northern hemisphere, although many are from the northern hemisphere. For the moment we can safely say that the majority are found in Australasia, and of these only some 15-20 species of Cyathea and 6-7 Dicksonia are commercially cultivated. The majority of tree ferns available in Europe are there at the behest of collectors of exotic plants, and therefore many nurseries or garden centers do not stock them. Sadly, many people, possibly the majority of indoor plant lovers, have no idea how delightful these plants are when grown in pots. The Dicksonia in particular will happily stay in a pot for many years, providing a lovely addition to the many other perennial, indoor, potted plants that the larger public enjoys. The colder climate of Europe restricts the growth of these plants so that they can be kept indoors and in pots for so much longer.

*Editor's note: From January 2001, Dicksonia antarctica is no longer covered by the CITES convention, and certificates are no longer required for either export or import.

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