Woodland and hedge banks, particularly damp places. Also meadows and stream-sides.
For more info see https://www.plantlife.org.uk/uk/discover-wild-plants-nature/plant-fungi-species/lesser-celandine
Lesser celandines (Ranunculus ficaria) belong to the buttercup family and confusingly they are not closely related to the greater celandine (which belongs to the poppy family)! There are two types of lesser celandine. The main difference is how they reproduce. Like snowdrops, there aren’t many pollinators around so early in the year, so one species produces bulbils instead of seeds. A bulbil is a tiny secondary bulb that forms in the joint between a leaf and the stem. As it is produced by asexual reproduction, it is exactly the same as its parent and not a mixture of two, like a seed. When ripe, the bulbils become loose and drop to the ground and each one can produce a new plant! Heavy rain can sometimes wash them from the plants and spread them along stream and river banks. They also reproduce from tubers (swollen underground stem or roots, like a potato). The tubers hang in a bunch, a dozen or more together and people thought they looked like a bunch of figs which is where their Latin name ficaria, is from). The tubers break off easily and each one will grow into a new plant and they spread very quickly!