Primula veris, the Cowslip
Primula veris, the cowslip, is a European wildflower that bears nodding, bright yellow flowers in the early spring. They are very hardy and fairly tolerant of unfavorable conditions.
On the roadside near my house, Primula veris has self-sown and mingles with blue and white violets, grape hyacinth, dandelions, and other spring flowers to create a display that is literally a traffic stopper.
The illustration on the left is Millet's Primroses (1867-1868).