Just For the Record

In all my (long) life, I can never recall having seen this plant before.

It is so unusual in form, that I am sure I would have remembered it if I had ever encountered it previously.

Google quickly identified it for me.
Here in the UK it is known as Winter Purslane or Springbeauty.
In North America, where it is native, it is called Miner's Lettuce.
Worldwide, it is recognised as Claytonia perfoliata.

The whole plant is edible, supposedly tastes like spinach, and is rich in vitamin C.  Its US name relates to its consumption during gold-rush times.

It was brought to the UK in the late 18th century, escaped into the wild and has since become naturalised.  It is widespread but local.

The circular 'collar' below the flowers is formed from two leaves fused together.