Ferns - California Wood Fern
Dryopteris arguta
The underside of the frond.
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These clusters of spores on the underside of the frond are called sori (singular = sorus). Each of the sori is covered by a membrane called the indusium.
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These sori are more mature.
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As the spores mature, the indusium shrivels, and then spores are released.
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