Indusium

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indusium

[in′dü·zē·əm]
(anatomy)
A covering membrane such as the amnion.
(botany)
An epidermal outgrowth covering the sori in many ferns.
(mycology)
The annulus of certain fungi.

Indusium

 

a small process on the leaf surface of ferns that covers the clusters of sporangia (sori). Indusia develop mainly from the leaf epidermis, from the placenta (on which the sporangia sit), or from the curled edge of the leaf.