Element Mendeleev originally found in flowering plant (9)
I believe the answer is:
germanium
'element' is the definition.
(germanium is a kind of element)
'mendeleev originally found in flowering plant' is the wordplay.
'originally' suggests taking the first letters.
'found in' means one lot of letters goes inside another.
'flowering plant' becomes 'geranium'.
The initial letter of 'mendeleev' is 'm'.
'm' going within 'geranium' is 'GERMANIUM'.
(Other definitions for germanium that I've seen before include "semiconductor material" , "Semiconducting element" .)