Lesser Celandine was actually in bud in December, but the early ones never open fully. The area where the first ones open is under trees in a south-facing stream-bank, so I suppose they're fairly well-sheltered and well-lit at the same time.
Lesser Celandine (which is, of course, a buttercup) is quite useful to me as it hosts a couple of the Uromyces rusts and various Phytomyza leaf-miners, so I can get looking for those very early on. A natural follow-on from the miners is the first appearance of the parasitic wasps - the ichneumonids. These are parasitic on the fly larvae in the mines, but I've often found them exploring the fungal rusts, too. I wonder if they're using the fungal spores as an early food source (I often see flies on tar-spots, etc., so I assume that they get some benefit from them.) That would be a handy self-contained food-web with the plant at the hub: plant hosts fungus; fungus feeds wasp; plant hosts fly; fly hosts wasp: