The common buttercup (Ranunculaceae).
A surprisingly resilient weed that has tendency to grow on lawns even during particularly wet or dry period.
In order to protect your grass, but still still ensure you get rid of your buttercups, Resolva Lawn Weedkiller is the best option. For buttercups in other places, use Resolva 24H.
Try spraying the weed when it’s about 10-15cm tall during its vigorous spring growth period.