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3052 Views 2 Replies Last post: Nov 20, 2013 3:01 PM by TRW RSS
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Nov 20, 2013 1:28 PM

Bracken Spores?  Galls?

2 photos attached, taken from 2 different locations at 2 different times this year.  Both on Bracken.  Would they be spores of some sort?  Any help, much appreciated

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    Nov 20, 2013 2:37 PM (in response to TRW)
    Re: Bracken Spores?  Galls?


    actually neither of your ferns are Bracken - what you have are the sporing structures on the Male fern (Dryopteris filix-mas) above and on Intermediate Polypody(Polypodium interjectum) below. The spore bearing structures, the sporangia are more easily seen on the polypodium because it does not have a protective cover (indusium) shielding them as they develop, unlike the Dryopteris which characteristically has a kidney shaped indusium which shrivels as the spores ripen and are released. The sporangia are clustered together into sori (singular sorus) - each of those small blobs in each cluster is a sporangium shaped a bit like a boxing glove - it has a narrow whippy stalk and an enclosed pouch which contains 64 minute kidney-shaped spores. Across what would be the knuckles of this glove are a band of thicker walled cells - the annulus - these have more thickening on one side than the other so as the ripe sporangium dries out an unequal tension is set up which eventually rips the structure apart flinging the spores into the atmosphere. If you multiply up all those 64s you realise that each fern frond will release tens of thousands, or more, spores each year. That we are not knee-deep in ferns is an indication that the development of new plants is not a very successful process!

    The details of these sporing structures and the spores themselves are very important for the identification of the species in these and other fern genera.

    Incidentally Bracken (Pteridium aquilinum) is unusual in that mature plants don't spore every year -sporing is very climatically dependant - most of Bracken's relatives being tropical and Bracken itself (and its spores) are very frost sensitive.

    Best wishes


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