A perennial, Autumn Hawkbit is a member of the Compositae sometimes mistaken for a Dandelion, but the leaves are finer and the deep lobes are symmetrical. Also the flower stalks are not hollow and may be branched. A more similar plant is Cat's Ear, but the leaves and stems of the latter have fine hairs.
The bright yellow flowers appear from June to October. The petals are squared at the tips with a serrated edge. They close up when pollinated and open again to release the seeds on downy carriers, but remain cupshaped not a full sphere like Dandelion.
The roots are many branched and do not go down deeply so it is easily uprooted.
A systemic herbicide like Glyphosate is best. Pull off any flowers as they can mature and produce seed before the chemical can act. In the lawn a selective weedkiller should work, or use Gylphosate as a spot weeder.