Gertrude —, landscape gardener (6)

I believe the answer is:

jekyll

(Other definitions for jekyll that I've seen before include "Doctor with another side to him" , "Doctor with an alter ego" , "Alter ego of 19 (Stevenson)" , "Famous novel 'Dr ...... and Mr Hyde'(6) ()" , "Robert Louis Stevenson novel 'Dr . . . . . . and Mr Hyde'" .)

I've seen this clue in The Times.

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