Billionaire invested in revolutionary American plant (7)
I believe the answer is:
chelone
'american plant' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'billionaire invested in revolutionary' is the wordplay.
'billionaire' becomes 'Elon' (tech billionaire Elon Musk).
'invested in' indicates putting letters inside.
'revolutionary' becomes 'Che' (Che Guevara the Marxist revolutionary).
'elon' put into 'che' is 'CHELONE'.
Can you help me to learn more?
(Another definition for chelone that I've seen is " North American plant".)