Download Ferns are a primitive group of land plants that first appeared in the

Ferns are a primitive group of
land plants that first appeared in
the fossil record towards the
end of the Devonian, about 360
million years ago. They were an important food source for dinosaurs that
roamed the Earth from 230 to 65 million years before present times,
although many fern families, genera and species did not appear until the
early Cretaceous 150 million years ago.
There are more than 12,000 extant fern species throughout the world,
found on every continent with the exception of Antarctica. They are
most abundant in moist tropical and warm temperate areas although they
can survive surprisingly low temperatures, and grow in all but the most
extreme hot, dry deserts. In Australia, there are almost 400 endemic
fern species.
Pteridophyte is a loose term that encompasses four major groups:
 Polypodiophyta (Filicopsida) True Ferns
and three clades that do not produce the conspicuous fronds we associate with
ferns:
 Psilophyta
Whisk Fern, Skeleton Fork Fern
 Lycopodiophyta
Lycopodiaceae
Clubmosses
Selaginellaceae
Spikemoss or Clubmoss
Isoetaceae
Quillworts
 Equisetophyta
Equisetaceae
Horsetails
Ferns, characteristically, have well developed
fibrous roots, stems (rhizomes) and green
leaves (fronds) connected by a vascular
system that is not present in mosses or
liverworts. This was integral to ferns moving
away from lakes, streams, bogs and rivers to
drier areas. Roots provide access to
underground water and nutrients, as well
as anchoring the plant to the ground,
while phloem transports sugars from
photosynthesis throughout the plant.
Development of a waxy layer (cuticle) on
the leaf surface limited water loss, and
stomates (leaf pores) enabled gaseous
exchange. As for shape and form, the
elegantly curled heads of emerging fern
fronds are a model for leaf development:
they are called fiddleheads, or croziers.
Like bryophytes, ‘true ferns’ reproduce by
spores which are mounted on the
undersurface of leaves in sporangia.
These, in turn, are usually aggregated into sori. The position of sori on
the undersurface of fronds and their characteristic shape are features
that are used by botanists to identify ferns.
Elongated sori on margins of fronds of Asplenium bulbiferum
Two sporangia in each sorus of Coral Fern
When spores released from the sori germinate on suitable, and usually
moist, substrates, they grow into what is known as a prothallus (a haploid
gametophyte); this is a small, delicate, usually heart-shaped structure
just a few mm across. Gametes (sperm and eggs) are produced from the
gametophyte, and, as long as there is a film of water across the
prothallus, mobile, flagellate sperm swim across the surface to fertilise
female egg cells, ultimately resulting in the development of the diploid
sporophyte. This will then grow much larger to become a readily
recognisable fern. Many species can also reproduce asexually from
sections of rhizome, and from plantlets that occur
on leaf margins.
Ferns can grow in a
great
diversity
of
habitats;
aquatic,
terrestrial,
epiphytic
(growing on trees or
tree branches), epilithic
(growing on rock). They
also
have
an
extraordinarily diverse
range of growth forms,
from tiny free floating
aquatic plants, to leafy,
Hymenophyllum dilatatum, a filmy fern
green herbaceous plants
to arborescent tree ferns that can grow many
Tree ferns can be many metres high
metres tall. Filmy ferns which have soft,
delicate leaves, often only a few cells thick, are often mistaken for
mosses or liverworts. Ferns, like mosses, don’t grow in marine
environments.
Ferns may be very decorative and are much sought after as house plants
but contribute much less to landscapes and global cycles than bryophytes
(mosses). One exception is the floating fern Azolla which hosts nitrogenfixing
cyanobacteria,
an
important,
sustainable
biological fertilizer in Asian
rice fields. And we should not
forget that ancestors of
modern
ferns
were
a
significant
component
of
Carboniferous and Permian
coal-forming ecosystems.
Australian National Herbarium, Canberra. https://www.anbg.gov.au/fern/taxa/pteridophyte.html
Australian Plants Society, Central Coast Group: http://www.australianplants.org/fsgseven.htm
Plantnet: http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=cl&name=FILICOPSIDA
Rainforest Australia: http://rainforest-australia.com/Rainforest_ferns.htm
Wikipedia: https://en.wikipedia.org/wiki/Fern
Alison Downing, Brian Atwell, Kevin Downing
Department of Biological Sciences