Plant that opens a route to a fortune (6)

I believe the answer is:

sesame

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'plant' is the definition.
(I know that sesame is a type of herb)

I don't understand the remainder of the clue.

(Other definitions for sesame that I've seen before include "Small oval seeds yielding an edible oil" , "Seeds used for making oil" , "Part of code for opening" , "Open ...... is magic phrase for opening door in pantomime" , "Seed used in flavouring" .)

I've seen this clue in The Irish Times.

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