Snake's head fritillary

Surely one of our prettiest native flowers? 
It wasn't described until the sixteenth century by Gerard, but then only as a garden plant. The first description of it in the wild wasn't until 1736. This led some to feel that it must be a garden escapee.
Generally it is now regarded as a native plant although Mr Grigson didn't think so.
The genus name derives from fritillus or dice-box and the specific from the apparent resemblance of the petals to guinea-fowl feathers.
The largest concentration of these in the UK is at North Meadow near Cricklade, Wiltshire in the Thames valley. The Magdalen College meadow in Oxford is another famous site and there's a stunning photo of it in Flora Britannica.