Crossword Genius

Herb in America caught opening leaf, oddly sheathed (8)

Ross

I believe the answer is:

cilantro

I'm a little stuck... Click here to teach me more about this clue!

'herb' is the definition.
(cilantro is a kind of herb)

I don't understand how the rest of the clue works.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.
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