Narrow-lipped Helleborine.
The Narrow-lipped Helleborine, is one that I have searched Dorset for over several years.
I understood that it had been recorded at 3 or 4 sites at the end of the last century and the only known plant that was in the RSPB site at Garston Wood had been destroyed!
I found this one plant this year (2010) in the Chase woods near there and on the border with Wiltshire.