Saturday, June 20, 2009

Rock Felt Ferns

Pyrrosia rupestris
We often see these little ferns growing on rocks and trees in the rainforests. Sometimes people mistake them for orchids, but here is one growing out at Gowrie Junction which clearly shows that it is a fern. It has these little brown spore- patches on the back of its fertile leaves (or “fronds”).
All ferns have two kinds of leaves, the infertile ones having no spore bodies. In many species of fern, the fertile fronds are a different shape from the infertile ones. Sometime the difference is hardly noticeable - they are just a bit longer and thinner. In the case of these little ferns, they are so different from the little round infertile leaves that they could be mistaken for the leaves of a different species of plant.
They are interesting, botanically, in another way, too. Green plants create their own food by photosynthesis. Using sun-power, they convert water and carbon dioxide into body mass. This means that they absorb carbon dioxide through their pores (“stomata”) whenever there’s enough light for the process.
Pyrrosia ferns are unusual in that they can absorb carbon dioxide at night and save it up for the daytime. They can therefore leave their stomata closed in the heat of the day to prevent themselves from losing water - a knacky trick which is the secret of their drought hardiness.
Rock felt ferns are quite easy to establish on trees in our own gardens. The best way to do it is to choose a tree with permanent bark, then wait for a light shower of rain, one which will partially wet the tree trunks without saturating everything. Examine your target tree, and note where the flow patterns of the water make wet patches. Choose a wet spot which faces east or south, so the little fern won’t have to cope with too much sun of drying wind, and attach the fern there.
Meanwhile, keep an eye out for spore bodies on the backs of the fronds of all kinds of ferns. There are a lot of them about at this time of year, and they are an easily overlooked delight, each species of fern having its own characteristic pattern.

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