Close-up view of the Japanese wood fern, Dryopteris erythrosora 'Brilliance'.


 

A Close-up View of the

Japanese Wood Fern


Dryopteris erythrosora 'Brilliance'

by Brian Johnston   (Canada)

Earth’s 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.

Dryopteris 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 ‘Brilliance’, has an identical growth habit, but possesses an even brighter colouration, which it holds for a longer period.

Dryopteris, the genus name, is derived from the Greek drys meaning oak, and pteron meaning a wing.  This refers to the shape of the fern’s 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 fern’s spore containing organs.

The first image in the article shows clearly the intensity of the coppery-red colour of the cultivar’s 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 fern’s 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 pinnules.



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 rachis.



As we move closer to a fiddlehead, it’s 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 leaflets?



At this stage, it’s difficult to be certain.  All of the Dryopteris erythrosora ‘Brilliance’ 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 purplish-brown.



Perhaps when we get still closer to the structures, a little later in the article, a solution will present itself.  For the moment, let’s 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.



It’s 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 place.



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 -


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 don’t 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 break apart.



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 pinna’s stalk is longitudinally grooved.



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 rib.



A view of the underside of a pinna reveals that the bumps are actually depressions in which the fern’s reproductive structures are located.



The thin, semi-transparent, horseshoe-shaped structures are protective membranes called indusia that cover the fern’s 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 – 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 fern’s reproductive structures, with images, please see my article concerning the Shield Fern – Dryopteris filix-mas ‘Crispa Cristata’.

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 fern’s 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.


Photographic Equipment

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 images.


Further Reading

About Ferns              http://www.home.aone.net.au/~byzantium/ferns/about.html

Backyard Ferns         http://www.backyardnature.net/ferns.htm

Fern Reproduction     http://www.bbg.org/gar2/topics/botany/repro_ferns.html

Fern Sporangium       http://www2.auckland.ac.nz/info/schools/nzplants/fern_sporangium.htm

Gardening Ferns        http://www.hgtv.com/hgtv/gl_plants_ferns/article/0,1785,HGTV_3604_3450395,00.html


A Flower Garden of Macroscopic Delights

A complete graphical index of all of my flower articles can be found here.


The Colourful World of Chemical Crystals

A complete graphical index of all of my crystal articles can be found here.


 All comments to the author Brian Johnston are welcomed.

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