There’s a flower that shall be mine, ‘Tis the little Celandine.
The lesser celandine is now in flower in our garden, along with the dandelions, but well before the buttercups come out. What a beautiful flower!
In the UK these flowers are a traditional harbinger of spring, typically the first flowers to appear in woodland. According to Wikipedia, the leaves of this attractive plant are poisonous if ingested raw, and it is regarded as an invasive species in parts of the USA and Canada, as it can succeed to the detriment of native wildflowers.
Also known as Ficaria Verna, pilewort (haemorrhoid remedy), fig buttercup.