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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