Partner following him? A plant (4)

I believe the answer is:

herb

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

I can't explain the rest of the clue.

(Other definitions for herb that I've seen before include "Basil, for example, is one" , "Parsley, sage, rosemary or thyme?" , "'Sage or rosemary, say (4)'" , "ingredient for recipe?" , "Useful or edible plant" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app