A thin membranous covering, especially a shield covering a sorus on a fern frond.
- ‘The upper surface of the intermediate portion of the corpus callosum is covered by a thin veil of gray substance - the indusium griseum.’
- ‘The latter is covered by the indusium griseum, a thin sheet of rudimentary cortex containing (on each side) the delicate medial and lateral longitudinal striae.’
- ‘The leaf margins themselves are often reflexed to form false indusia that protect the sori.’
Early 18th century: from Latin, literally tunic from induere put on, don.