Fritillaria meleagris ('Snake's head fritillary) is a British native plant and flourished in our Cambridge garden but is obviously not partial to our heavy Pennsylvania clay and harsh winters.
Fritillaria pyrenaica is native of the Pyrenean meadows and is supposedly one of the easiest and most rewarding fritillaries to grow. It flowers just as F. meleagris fades and is meant to bulk up to form substantial clumps and even self-sow when happy. It obviously is not happy in my garden, but at least more than one seems to have survived. It is usually a dark brown with a dull gold lining that's just visible when the segment tips curve outwards. Like most fritillarias they gave a rather spunky unpleasant odour, but if I could grow them successfully I would still plant more.