I first noticed this strange Arum-like plant a few years ago. It was growing on the banks of the the top lake just below the pile of boulders that is known as the Grotto. I had some difficulty in identifying it as it was obviously not a native to the UK. I eventually found it mentioned in this post on the Whiteknights Biodiversity blog at Reading University as Lysichiton americanus, otherwise known as western or yellow skunk cabbage because of its smell (though I didn't notice an particularly strong smell while taking these photos). It is a member of the Aracea, the Arum family.
This is a close-up of the tiny flowers:
Photos taken in the Wilderness, Whiteknights Park, Reading, UK, on 2014-04-06.