Posted by: Rob Viens | April 16, 2012

The 300-Million-Year Legacy of Tree Ferns

Limiting his stay at the unpleasant estate of Mr. Lennon, on April 16th Darwin turned around and returned to Signor Figuireda’s fazenda.  (At first I thought this was a new estate, but upon careful reading it does seem to be the same place he wrote in detail about on April 13.) Apparently he is now on a first name basis with the owner:

“Started early in the morning to Signor Manuel at Socêgo, whom it was agreed upon should be arbitrator: Again I enjoyed the never failing delight of riding through the forests.” (Apr16)

As often is the case, what strikes me about his entry today is Darwin’s shear joy at being in the forest – enthralled by birds, insects, and plants.  During his description of this part of the trip in Voyage he notes:

“The forest abounded with beautiful objects; among which the tree ferns, though not large, were, from their bright green foliage, and the elegant curvature of their fronds, most worthy of admiration.” (Voyage of the Beagle)

“Most worthy of admiration” indeed – these little “trees” have a history that goes back over 300 million years to the Devonian Period. Long before the age of conifers and flowering plants, the tree ferns grew alongside giant horsetails and club moss “trees”.  It is forests such as these from the Carboniferous Period that were the source of some of the most extensive coal deposits of today – sunlight stored underground for more than a quarter-of-a-billion years!

Some of the more modern families of tree ferns later stood among the cycads and conifers of the great Jurassic  forests of Gondwana. Although the species are not quite the same, the basic structure of the tree fern has not changed much since that time.

Carboniferous forest. From: Smithsonian Museum (Mary Parrish, artist)

Carboniferous forest

The term tree fern is relatively generic and can be used for any fern (class Polypodiopsida) that grows on a tall stalk (like a tree).  Though, the term is more specifically used for two families of ferns today (Dicksoniaceae and Cyatheaceae). They don’t actually grow like the trees we are familiar with – the “trunk” is not made of wood.  In fact, it is more of a mass of “roots” (technically a rhizome or “rootstock” from which roots grow) that elevate the fronds above the ground.  And, like all ferns, they reproduce via spores, rather than seeds.

There are hundreds of species of tree fern living today, and even though Brazil only has a fraction of these species, I have no idea which specific type Darwin was describing.  They are all “beautiful”.  One example (though not from Brazil) is Cyathea cooperii from the Azores (from an excellent post from the blog Future is written in green – check it out!)

Brazilian tree fern

Like so many ancient plants, tree ferns have had a rough time of it in recent years. Between deforestation (extreme habitat loss) and collection for the plant trade, their numbers have declined (and some species have gone extinct).  I suspect that climate change will have an impact on them, too. No doubt, future naturalists will curse us for decimating a 300-million-year legacy. (RJV)

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Responses

  1. […] So I thought I’d take this opportunity to add a little more to the discussion on tree ferns from a couple of days ago. […]

  2. […] km2 (though I’m not sure how they define this claim). (For more on tree ferns, be sure to see The 300-Million-Year Legacy of Tree Ferns and Tree Ferns […]


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