Meadow Buttercup

Perennial spreading by seed and short creeping runners which form new plants - this vegetative spread is limited due to the shortness of these rhizomes. The seed can remain viable in the soil for several years and germinate after cultivation. It is not usually a problem in lawns, it forms a rosette with the growing point at soil level, so it can resist mowing, but it is not very tolerant of trampling; the Creeping Buttercup is usually the problem lawn weed.
Grazing animals usually avoid it as they can suffer from abdominal pain and inflammation leading to diarrhoea caused by a toxin ranunculin in the fresh plant, but it becomes denatured in dry material so is not a problem in fodder. It is thought to deplete Potassium in the soil, so having a detrimental effect on surrounding plants (allelopathic).
The palmate leaves are deeply divided, almost to the base into three lobes and these are deeply cut as well. They can look very similar to some of the Hardy Geraniums.
The bright yellow flowers have five shiny petals and occur from May to July. They are borne on an unfurrowed, branching stalk which can be up to 30cm tall. After pollination by visiting insects about 30 seeds develop in a spherical fruit. The seeds have a short hook or achene.

Dig out, following the runners to remove any which have taken root; the white, fibrous adventitious roots do not regrow, but ensure that the growing point is removed. Cutting at an angle under the rosette will sever the tenacious roots and it is easily removed. They prefer the moist conditions of clay soils, so improving drainage will help to eradicate them.
Weedkillers to use:-
Glyphosate, systemic action killing the whole plant. Apply as spot weeder in the lawn. Treat the whole lawn with a selective weedkiller on its own ( eg. Verdone Extra) or a weed-and-feed type, it will probably take two or three applications to eradicate it because of the reservoir of seed and more mature plants may recover. Some variants have developed resistance to MCPA.

See also Creeping Buttercup which is very similar.

Follow these links for further details on Weeds, Weed Removal and Weed Prevention.