Species of the Week
Number 28 --
February 19, 2007

In the Species of the Week feature of the Wildwood Web we took a close look at one of the species that lives in Wildwood.  To see the earlier featured species check the Species of the Week archives.


Wall Rue

Asplenium ruta-muraria

Not all evergreens are coniferous trees.  A number of ferns are evergreens.  The ferns which have starred as Species of the Week so far, Christmas fern and walking fern, have both been evergreen.  This week we will look at a rare evergreen fern that hardly even looks like a fern: wall rue.  The common name comes from the fact that the leaves look the leaves of the bitter herb known as rue, and it likes to grow in crevices in limestone boulders and cliffs.  It is a small delicate fern, with two to four pairs of leaves divided into somewhat triangular leaflets with scalloped or tattered-looking edges.  To me, it looks like parsley.

Wall rue likes shady boulders in limestone regions from southern Ontario to Quebec south through New England and the Appalachian Mountains.  It is also found in isolated populations along the shores of the Great Lakes and in Missouri and Arkansas.  It is also native to Europe and eastern Asia.  Despite this wide range, it is not common, according to Broughton Cobb, author of the Peterson Field Guide to the Ferns.  It appears to be quite rare in Wildwood, being found, as far as I know, on only two boulders on the eastern slopes of the Park.  It is not hard to find, if you look for improbable parsley plants.  Should you find it, please do it no harm.  Should you find more plants than two, please let me know of them. 

Ferns of the genus Asplenium are known as spleenworts because some members were long thought to be useful in the treatment of diseases of the spleen.  As far as I know, this is a mistaken belief.  The genus name, not surprisingly, comes from the Greek word for spleen.  The species name ruta-muraria is simply Latin for "wall rue."


We have already met a spleenwort in Wildwood; walking fern is also an Asplenium.  Wall rue and walking fern have been reported to hybridize, producing offspring which Merritt Fernald describes, in Gray's Manual of Botany, as having triangular leaves with long extended tips like walking fern, but divided into leaflets at the base like wall rue.  This oddball fern has been given the scientific name of Asplenium x inexpectatus, which translates as "unexpected Asplenium."  The x in its name is botanical code for a hybrid between different species.  As you wander Wildwood looking for wall rue, keep an eye out for this odd looking hybrid.  It would be fascinating to find this unexpected fern among Wildwood's treasures.



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