A close up view of the Japanese painted fern.

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 colourful fronds.

Athyrium goeringianum ‘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.

Athyrium goeringianum ‘Pictum’ or Athyrium niponicum ‘Pictum’ as it is alternatively called, is a cultivar of Athyrium niponicum, a plant native to Japan (hence niponicum), Northern 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). It is obvious that each pinna is composed of smaller sub-leaflets. These are called pinnules (singular pinnule). 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 colouration.

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 their ages.

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 the pinnules.

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 serrations.

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. The 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. For 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!

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.

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