A close up view of the Japanese painted fern.
View of the
Japanese Painted Fern
by Brian Johnston (Canada)
The present article is one of four that
take a close look at fern species. In order to reduce overlap as
much as possible, each article focuses on only those characteristics
that make the particular fern distinctive – in this case the fern’s
‘Pictum’ is one of the most popular cultivated
ferns. This fact is not surprising when you consider the
extraordinary colouration of its fronds. Depending on their age,
the leaflets may display a pallet that runs from green, through
metallic silvery-gray, to deep maroon. The fronds do indeed
appear to be ‘painted’. It is interesting that the deepest
colouration is produced when the fern grows in light shade; excess
sunlight tends to mute the colours.
‘Pictum’ or Athyrium
niponicum ‘Pictum’ as it is alternatively called, is a cultivar
of Athyrium niponicum, a
plant native to Japan (hence niponicum),
China, Korea, and Taiwan. The fronds of the native plant
tend to be from 25 to 40 centimetres in length, while those of the
cultivar tend to be somewhat shorter. Both ferns have fronds that
droop, a characteristic referred to as a weeping habit.
A single leaf, or frond is shown below. The deep
maroon stem that supports the leaflets is called the blade or rachis of the fern. Each of
the larger-scale leaflets is referred to as a pinna (plural pinnae).
is obvious that each pinna is composed of smaller
sub-leaflets. These are called pinnules
Because the frond has both pinnae and pinnules, it is referred to as twice-divided, or twice-cut.
Younger pinnules tend to be greener
than older ones, and display more contrasting vein structure. The
‘older’ frond shown on the right, below has a paler green
Front (left) and back (right) views
of a frond are shown below. Note that the front of the maroon
rachis has a distinctive longitudinal groove, while the back does
not. Notice also that the back surfaces of pinnules have a
brighter green colour than the front.
The pinnules of the Painted
Japanese Fern often overlap one another, as can be seen in the images
that follow. Their outer edges tend to be serrated, with
moderately sharp points.
In a clump of ferns, the fronds,
naturally, possess different ages. This results in their having
different colour pallets; younger ones tend towards green and maroon,
while older ones tend towards silvery-gray and maroon. The closer
the viewer is to the clump, the easier it is to distinguish between
The two images that follow show
this difference very clearly. Older fronds are positioned on the
left, while newer ones are on the right.
An older frond is shown at the
centre of the two images below. Notice how it droops, conforming
to the weeping habit.
The stalk (rachis) that supports
the pinnae is grooved on its front surface, as is the one that supports
Here are two views of an older
pinna, with its component pinnules. The pinnules have a vaguely
“paw-like” shape, with a convex top surface.
At the high magnifications of the
macro-photographs below, even the cellular structure of a pinnule
becomes visible. Notice the colour and shape of each of its
Details of the front surface of the
grooved stalk that supports the pinnules, can be seen below.
Unlike flowering plants which
usually contain male stamens and female pistils, ferns have a different
reproductive strategy. They produce spores that grow into tiny plantlets
called gametophytes providing
that the environmental conditions are suitable. If we look at the
reverse side of one of the pinnae in the mid to late summer period, the
fern’s reproductive structures are visible in rows beside the main
veins of the pinnules.
The horseshoe-shaped, off-white
structures seen in the image below are membranous protective coverings
for the spore producing organs. Each is called an indusium (plural indusia). In this fern the
indusia are arranged in a herringbone pattern.
Under each indusium is a clump of
tiny spore-containing spheres called sporangia.
clump of spheres is referred to as a sorus.
Put simply, the
protective indusium covers the
sorus which is composed of many
sporangia which, in turn,
contain the plant’s spores.
views of sporangia and their spores, please see my article
concerning the Shield Fern –
Dryopteris filix-mas ‘Crispa Cristata’.
For comparison, here are images of
a similar area on another frond taken in the early spring, before the
development of the indusia, and associated structures has begun.
Few ferns are as ornamental as the
Japanese Painted Fern. To appreciate its charms fully however, it
is necessary to take a really close look!
The low magnification, (to 1:1),
macro-photographs were taken using a 13 megapixel Canon 5D full frame
DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.
An 8 megapixel Canon 20D DSLR,
equipped with a specialized high magnification (1x to 5x) Canon macro
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the
A Flower Garden of
A complete graphical index of all
of my flower articles can be found here.
The Colourful World of
A complete graphical index of all
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the April
2011 edition of Micscape.
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