indusium
noun
in·du·si·um in-ˈdü-zē-əm 
-ˈdyü-,
-zhē- plural indusia in-ˈdü-zē-ə
-ˈdyü-,
-zhē- : an investing outgrowth or membrane
especially : an outgrowth of a fern frond that covers the sori
Word History
Etymology
New Latin, from Latin, tunic
First Known Use
1807, in the meaning defined above
Medical Definition
indusium
noun
in·du·si·um in-ˈd(y)ü-z(h)ē-əm
plural indusia -z(h)ē-ə
: a membrane serving as a covering
especially : indusium griseum