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A covering membrane such as the amnion.
An epidermal outgrowth covering the sori in many ferns.
The annulus of certain fungi.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
But this instance does beg the question: Could the tokoloshe be the experience of a stimulated indusium griseum?
The epidermis of the indusium is a poorly studied character in species of Blechnum, but it can bring specific information (Rolleri and Prada 2006b); in the case of B.
Rhizomes long, creeping; fronds 35-70 cm long; blades 15-30 cm long, broadly triangular, long pointed apex, pinnate-pinnatifid; sori round, marginal; indusium lacking.
ATHYRIUM {eh-THIR-ee-um} Roth 1799 * Lady Ferns * (Greek athyros, doorless; sporangia tardily pushing open margin of indusium.]
Leaves with transparent, needlelike (pointed-tipped) hairs that are simple to branched; sori with or without indusium; rhizome creeping (mostly subterranean) and slender, less than 1 cm in diameter Thelypteridaceae (in part)
alabamensis Iwatsuki (Iwatsuki, 1964)] is a perennial, evergreen fern with rhizomes that produces spores year-round; it is the only taxon of Thelypteris in southeastern United States lacking an indusium (Crawford, 1951; Kral, 1983).

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