Close-up view of the Japanese wood fern, Dryopteris
Japanese Wood Fern
by Brian Johnston (Canada)
Earthís fossil record provides ample
evidence for the extraordinary success of the fern family. The
earliest ferns predate the Mesozoic era, some 360 million years
ago. Older than the dinosaurs, they were thriving several hundred
million years before flowering plants evolved.
erythrosora is native to eastern Asia, and has several common
names including Autumn Fern, Japanese Wood Fern, and Japanese Shield
Fern. Its main claim to fame is the very unusual (for
ferns) coppery-red colouration of its new growth. As the
plant matures, its colouration returns to the normal green of most
ferns. The cultivar studied in this article, Dryopteris erythrosora ĎBrillianceí,
identical growth habit, but possesses an even brighter
colouration, which it holds for a longer period.
name, is derived from the Greek drys
meaning oak, and pteron
meaning a wing. This
refers to the shape of the fernís leaflets. In addition to the
this, the Greek pteris was
used by ancient Greeks for all ferns. The species name erythrosora translates to red
sori, and describes the colour of the fernís spore containing organs.
The first image in the article
shows clearly the intensity of the coppery-red colour of the cultivarís
new growth. In the foreground, several fronds display the
greenish-bronze tint of the next stage, and the image that follows
shows their final colouration. The fernís leaves, or fronds, are a glossy bright-green
colour, and are composed of leaflets called pinnae which are subdivided into
smaller leaflets called pinnules
that have slightly serrated edges. The pinnules are positioned on
the stalk in such a way as to produce minimum sized gaps between
them. The image below shows a single pinna with its component
New growth manifests itself as a fiddlehead (crosier) which has a distinctively
curled top. The name is used because of its resemblance to the
end of a violin or fiddle. Three such fiddleheads can be seen in
the foreground of the image below.
Two closer views of a fiddlehead
follow. Notice the scaly, black-tipped hairs on the stalk, or rachis as it should be called.
As a fiddlehead unfurls, you can
see the immature leaves arranged in an opposite orientation on the
As we move closer to a fiddlehead,
itís obvious that this is a strange and colourful structure.
Stranger than one might think in fact! What are the tightly
packed, bright red, bulbous formations on the ribs of the olive green
At this stage, itís difficult to be
certain. All of the Dryopteris
erythrosora ĎBrillianceí plants at my local Garden Centre
displayed the same colourful formations in the early spring. As
you can see from the images, each appears to have a red, bulbous base,
and a single, flattened, narrow triangular hair at its top. As
time passes the base diminishes in size ,and its colour intensity
diminishes. At the same time, the hair-like top darkens to a
Perhaps when we get still
the structures, a little later in the article, a solution will present
itself. For the moment, letís look at what happens when the
fiddlehead begins to uncurl. Here is what it looks like.
As the stalk straightens out, the
individual leaflets also begin to uncurl, and slowly flatten.
They are still an olive green colour, but the details are obscured by
the attractive mystery objects. The centre of the image on the
right gives our best view so far of these objects.
The images that follow show two
views of a single unfurling leaflet.
Itís easy to resolve the cellular
composition of the bases of our mystery objects.
At this stage, the leaflet shown
below has almost completely flattened. Look at the stalk.
It appears as though the bulbous bases of our mystery objects have
deflated, turned light brown, but still have their hair-like top in
Here are two views of a leaflet
(pinna), with its sub-leaflets (pinnules). Notice that each
pinnule has a semi-circular scalloped edge.
The images below show the maximum
magnification of our mystery objects possible with my
macro-photographic equipment. After consulting with a number of
fern experts about these strange formations, it is obvious that they
are very unusual. To summarize their ideas -
- They are normal, but
- They appear to be
hypertrophied (enlarged) bases of the scales that are commonly present
on the root, rachis and leaflets of this genus (Dryopteris).
- There are two kinds of scales
- some scattered, slender, dark-centered scales, and the abundant red
"bullate" scales (meaning that they are arched, inverted, and almost
Here is a photomicrograph showing
the bulbous base of one of the objects.
The following images were obtained
from a different part of the fern clump. Notice the extremely
tiny, white, cellular, hair-like structures growing from the
undersurface of the pinnule. These have no bulbous base.
Strangely, the shape of
pinnules depends on the location of the pinnae along the main stem
(rachis). Notice that those shown below donít possess the
scalloped edges of the ones seen earlier. In the photographs, the
bases of the mystery objects have faded to a pinkish-brown colour.
Some pinnules have a stalk, albeit
a broad, very short one.
The photomicrograph below shows the
cellular structure of the base of a mystery object as it begins to
Earlier in the article, I mentioned
that the intermediate colour of the pinnules is bronze. Here is
an example. Note that the front surface of the pinnaís stalk is
A mature pinna, like the one shown
in the three images below, has a glossy green colour.
About a month after the previous
photographs were taken, I observed an orderly pattern of bumps
appearing along the main rib of pinnules.
Higher magnification reveals that
most, but not all, are positioned in pairs, on opposite sides of the
A view of the underside of a pinna
reveals that the bumps are actually depressions in which the fernís
reproductive structures are located.
The thin, semi-transparent,
horseshoe-shaped structures are protective membranes called indusia that cover the fernís spore
containing organs. These organs can be seen through the membrane
as a light green arc around the centre of each indusium. The
group of organs forming the arc is called a sorus. If the species name
of this fern is erythrosora Ė
red sorus, why are these not red? I suspect that since the
photographs were taken in the early summer period, these may be
infertile, and not the red, fertile ones that appear in the late summer
and early fall. (This is only a guess however.)
For a more detailed description of
a fernís reproductive structures, with images, please see my article
concerning the Shield
Ė Dryopteris filix-mas ĎCrispa Cristataí.
When I first found the Japanese
Wood Fern in May at my local garden centre, I assumed that the
brilliantly coloured structures that peppered many of its surfaces were
just a normal part of the fernís makeup. It was only when I
started to write this article in late October of the same year that I
was unable to find any images, or mention of, these structures.
My requests for assistance were all answered with enthusiasm by very
knowledgeable amateur and professional botanists, and I would like to
express my appreciation to them for
taking the time to help me out.
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.
- The cause or reason for the
malformations is uncertain. It could be something environmental -
such as extreme cold, or a chemical treatment at the garden centre that
drifted over the plants.
Microscopy UK or their contributors.
Published in the March
2011 edition of Micscape.
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