Friday, March 26, 2010

Skeleton fork-fern

Psilotum nudum
The story of the evolution of plants is full of interest and unexpected turns.
Here’s a thing which has often been described as “a plant that evolution forgot”. It so closely resembles the fossils of the world’s first vascular plants that it was thought that it had simply found itself so well able to survive, in its large range of native habitats, that it hadn’t needed to change for some 400 million years.

(Vascular = “with vessels” - the plant equivalent of our own blood vessels. Vessels carry nutriment from one part of the plant to another, and this evolutionary “invention” was the one which allowed land plants start getting height. Up till they evolved, the only plants had been non-vascular ones like algae, mosses and liverworts. The only large non-vascular plants are giant seaweeds. Modern vascular plants, descendants of the skeleton fork-fern’s look-alike ancestor, include ferns, conifers and other trees, grasses, and all the other flowering plants.)

The skeleton fork-fern is not really a fern at all. Like the earliest vascular plants, it is very simple. It has no roots - only some underground stems - no leaves, no flowers, and no seeds - just these strange (and decorative) little yellow spore cases.

As it has no roots, it couldn’t survive without its the mycorrhizal soil fungi, which attach themselves to its underground stems and provide it with the nutrients.
Yet it is a highly successful survivor, growing in warm and cool climates all around the world, and living in habitats from swamps to dry rocky cliffs.
Evolution didn’t forget it, though. Recent molecular evidence has shown that the skeleton fork-fern is actually a highly evolved organism, a descendant of some true ferns. This plant’s ancestors actually had roots and leaves, but has evolved beyond them. It has taken an evolutionary trail which at first glance seems regressive, but you can’t argue with that kind of success!
You will have your own opinion as to whether it is attractive enough to grow it in your garden. I like its much-branched green stems, and its yellow spore cases that look a little like small wattle flowers.
Even if I didn’t, I’d probably want to grow it just because it’s so interesting.

1 comment:

Anonymous said...

Thanks for the information. I found this thing growing like a weed in my Aloe Vera pot. I removed it because it was taking over. Maybe I'll re-pot it if it comes up again.