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Index of Subjects Still interested in the origin of the 'Sensitive Fern' rings on the Mt Uniacke estate, on a recent visit to UK I mentioned this to a colleague. He had been in S. Africa with a biologist there, who in turn had had some involvement with the Namibian fairy ring phenomenon. In a low rainfall zone in a remote Namibian desert, there are thousands of these circular depressions of bare sand up to 30 feet across in 'colonies', each surrounded by a fringing ring of desert grass that is more luxuriant than that in the clumps lying between the rings. Ring origin is uncertain but one recent research suggestion is that certain sand termites eat the grass from the middle of the ring outwards and kill it, so the centre retains no grass at all. The centre therefore is able to collect and retain precious rainfall water just below the surface for use by the termites, water that elsewhere gets taken up rapidly by root systems of the grasses. The grass at the edge of the circle has partial access to this reservoir so becomes lusher and available as termite food. The rings can last for up to 75 years but eventually each disappears, individually. If you?re not aware of these fascinatingly bizarre structures (I wasn?t), type ?Namibian fairy rings? into Wikipedia or Google. These particular termites are stylized by researcher Juergens as even more effective water engineers than beavers, which might raise a few eyebrows here. The S. African biologist e-mailed back that he did not know about fairy rings involving ferns, but had turned up a reference to a N. American fern that I?d missed: http://www.blueplanetbiomes.org/lady_fern.htm This site refers to the Northern Lady Fern (Athyrium filix-femina), a common native species and ornamental, which according to this site often forms fern rings, though no further reference for this is cited. Trying to pursue this on Google turned up several interesting medicinal uses by native peoples, but failed to reveal any other citations of Athyrium ring formation or speculation about the mechanism. Have any of the botanists on this list run across any more information, for Athyrium, or for Osmunda mentioned below? Somehow this led to the Interrupted Fern (Osmunda claytoniana). In Wikipedia, it is said to form small, dense colonies, each spreading locally through a very large rhizome, and it is said also to often form fairy rings. So at least in this case, there is some possibility of a mechanism, in that an extended rhizome might use up essential resources (nitrogen?) at its centre. It might then give rise to above-ground fronds in a ring but only at the still-resourced edge of the rhizome, as I think Dave Webster originally suggested. If this is correct, the consequence would be that each fern ring actually is a clone of genetically identical individuals. Apparently this is true for other ferns with rhizomes, and for some plants like goldenrod that also spread through rhizome colonization. Perhaps everyone but me knew this already. Steve (Halifax)
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