What is this grotesque 'thing'?

Many prayed it had been buried for all eternity after being shot by a silver bullet, but a simple villager looking for a few groats during these tough times has prised open the lead coffin that has kept Mystery Guess at bay for months only to reveal its horrendous form once more. Back to cause you sleepless nights and untold terror, Mystery Guess is my close-up picture guessing game. How do you play? Let me explain the rules. I've taken a close-up picture, cropped it and you have to guess what it is. Simple. I spotted this grotesque 'thing' on a recent visit to RHS Wisley in Surrey. As usual, there are no clues and no flashy prizes for winning. But guess correctly and you will join an esteemed list of former winners in the Mystery Guess Hall of Fame. I'll post the answer in a couple of days. Over to you…let guessing commence.