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Worldwide there are over 12,000
species of ferns.
The Wet Tropics is home to 65%
of Australia's fern species.
In Australia there are 390
native species of ferns, 47 species of fern allies, 44 species of conifers
and 39 of them are endemic.
Forty fern species are endemic to the Wet
Epiphytic ferns are one of the
most common features in rainforests.
They grow on the trunks and
limbs of trees but unlike parasitic plants such as mistletoe, do not steal
nutrients from their host tree.
They survive instead on
rainwater and the nutrients they get from trapped fallen leaves.
Visitors often mistake them
for bird’s nests, tree parasites, or part of the tree.
It is not uncommon to see
a large number of both species and individuals on the one tree.
Many can grow
to a size where they are larger in diameter than the tree that supports them.
Sometimes the host tree taps
into the fern though. Roots have been found growing from the host tree
into the epiphytes.
Evolution of Ferns
'Most ferns love the tropics
where the warm moist conditions, not unlike those in which they evolved, suit
their requirements. As a result the Wet Tropics is home to a wide range of
relict ferns- species which have survived from the earliest times. They
represent all the major evolutionary fern groups.'
In the evolutionary development
of plants, ferns represent a great advance on all previous models. The
surface cells of aquatic algae are able to absorb nutrients and water, on
land it is necessary to divide up the tasks, a step which makes the plants
- Roots were a revolutionary new feature
dedicated to seeking out less accessible sources of water, thus allowing
plants to move inland.
- They also served to stabilise the larger
- Water and nutrients, taken up by the roots,
had to reach other parts of the plant so a plumbing system - the vascular
- Woody vessels (xylem) performed this function,
moving water and nutrients upwards.
- These vessels had a duel function, providing
rigidity to the tissues.
- With these load-bearing structures the plants
were able to grow much taller and reach up to the light.
- Another plumbing system was needed to move the
sugars and other photosynthetic products from the leaves to the rest of the
- This function was performed by another new
system of vessels, the phloem.
Leaves and Photosynthesis:
- Leaves were another fern invention - a system
solar panels dedicated to capturing the energy of the sun and turning it
- Exposed to the air, these had to be sealed to
prevent the water gathered by the roots from leaking away so a waxy skin
(cuticle) was developed.
- Since the process of photosynthesis requires
an intake of carbon dioxide from the atmosphere and waste oxygen must be
released, special design features in the cuticle - pores - allowed this
exchange of gases to continue.
Other Early Vascular Plants:
- Although ferns were among the earliest
vascular plants (algae, lichens, mosses and liverworts are all classified as
non-vascular plants) they were not the only ones.
- The fossil records tell us that at one time
the world was dominated by massive clubmosses, giant horsetails and others
which created magnificent forests 45m or more in height as they used their
newly developed vascular systems to reach higher and higher in competition for
- Many of these plants are now extinct, their
relatives hanging on comparative obscurity.
Sexual links with the past
Although ferns are structurally more advanced than mosses, like the more
primitive algae and mosses their sex life involves two generations and a
dependence on water.
Spores are produced by the fern plant in spore cases, usually beneath the
When released, each spore grows into a tiny heart-shaped structure known as
the thallus which, in turn, produces male sperm cells at the pointed end and
female cells in the notch.
the presence of water, the sperm burst free from the thallus and, attracted
by chemicals, swim to the female cells.
Following fertilisation, an adult plant develops, eventually dwarfing its
Curiously this large spore-producing fern plant is the equivalent of just
the tiny spore capsule and stalk of the moss plant while the much more
obvious green moss plant is the equivalent of the tiny fern thallus.
Both produce sex cells.
Many ferns can, of course, increase their numbers asexually by spreading
their rhizomes-stems which are either below the soil surface or just above
Roots grow down from the rhizomes while fronds sprout from the top.
Courtesy of: Environmental Protection Agency, Cairns.
- While many of the plants in the rainforest have
been around for millions of years, ferns have been around for much longer than
that! They appeared in the fossil record dating back to 325 million years ago.
- They are one of the earliest vascular plant forms on the planet (plants which
circulate water internally) and they preceded the flowering plants, the conifers
and even the cycads - all of which have a more advanced means of reproduction.
These plants have a long fossil
record, and are usually thought of as the most primitive of all vascular plants.
They differ from ferns by lacking the large leaf-like fronds, and the spore
containing sporangia are found on the terminal ends of the leaf rather than on
the underside as in most fern species (Jackes and Cairns 2001).
Back in the
Carboniferous period, even before the dinosaurs, some species in these groups
grew as large as trees, and often comprised the dominant vegetation.
are found all over the world, but only as small obscure species.
Cycads were one of the dominant
plant forms back in the Mesozoic, the 'Age of the Dinosaurs', when they would
have comprised much of the forest as flowering trees do today.
Many species of
cycads are toxic, containing the lethal compound macrozamin (including the
species found in the rainforests here), and it has even been suggested that this
high toxicity initially evolved in this ancient group to deter predation by
However in the present day cycads are fairly restricted and less than
a few hundred species survive in the tropics and subtropics of the world.
usually have a trunk with the new leaves coming out only from the top, and thus
superficially resemble palm trees.
Howevor they are not true flowering plants,
but gymnosperms, and reproduce with cone-like structures.
Courtesy of Damon