Broom

Not the sweeping kind, the plant kind. Whole hillsides of it are opening up (Those not nibbled by cows and sheep anyway.) in a glorious display of firework yellow.

Do not confuse broom (soft, leafy semi-shrub, bright yellow flowers.) with gorse (hard, spiky, made-of-nothing-but-thorns with bright yellow edible flowers.), especially when diving into a mass of it. (It's happened, not pretty.)