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This Japanese cypress in Shiratani
sports a glowing crown of filmy ferns. |
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The spot called the "Moss Forest,"
wouldn't look so mossy without
its filmy ferns . |
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Leaves so thing the light shines
through are supported by
a network of viens. |
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Several species can
be found in Yakushima. |
| While hiking through Yakushima's old-growth forests, look up at the
spreading branches of ancient trees, caked with layers of spongy green
moss. But look again. Is moss the only thing up there?
From
towering tree ferns reminiscent of a prehistoric jungle to large forked sprays
fit for New Years decorations, ferns abound in
Yakushima from the coasts to the mountains. However, when hiking through the dark and damp, lush and
mossy forests, one of the most prolific, visible, and very beautiful
families often goes overlooked:
The Filmy Ferns
(Hymenophyllaceae)
I suppose it really shouldn't be a surprise that this family is often
clumped together with unrelated mosses by the casual hiker. Many filmy
ferns have leaves that are roughly the same size and shape as a sprig of
moss such as Plagiochila pulcherrima (ウツクシハネゴケ, literally "beautiful
feather moss"). And filmy ferns have similar growing habits: They thrive
in moist places. On humid days, the leaves fan out, and on dryer days,
they shrivel up.
If you look up at the sky through the leaves
of a filmy fern or moss, you can see sunlight seeping through. Beautiful. Both mosses and filmy ferns seem to glow in the sunlight, especially after a good rain. The body
of these translucent leaves is (with few
exceptions) only one layer of cells thick. They lack a waxy epidermis and pores (stomata) that allow many so many plants to breathe without drying out.
There are about
fifteen species of filmy ferns recognized in Yakushima. Of these, seven
species belong to the genus Hymenophyllum. They are easily confused with
each other, and I can't yet keep them straight, but let's not confuse them with mosses!
If you are not sure what is moss and what is a filmy fern, you
are in good company, but if you consider the size of the leaves, it becomes immediately obvious: This simple vascular systems of mosses they can (usually) only
support leaves on the scale of millimeters, or less. One leaf of the
filmy fern Hymenophyllum barbatum (コウヤコケシノブ) is roughly the size of a
whole specimen of P. pulcherrima, consisting of hundreds and hundreds of
leaves.
Another difference is the stems. Again,
because of lack of a vascular system, mosses don't tend to have long
dangly stems between leaves, but the leaves of filmy ferns are connected
by creeping, threadlike stems, and one plant can cover quite a large area.
No matter how much area they cover and how dense they grow, both mosses
and ferns readily dry out and shrivel when a dry spell comes through,
but will perk up again with a little rain. Many people feel that the
Moss Forest is most
beautiful when the sun comes out right after a shower and shines through
all those refreshed layers of
green, but after a couple days of sun, the effect is lost.
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Close up of part of a leaf. The body of the leaf
is one cell-layer thick. |
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