Bluebells

Each spring here sees a remarkable sprouting of indigo across the woods: bluebells, which bloom profusely until the overhanging leaves grow back in full, and the forest floor grows dark again. Other places in the world see such an annual blossoming, but few have such uniformity, for a simple reason.

As glaciers a mile deep retreated from Ireland and plants and animals migrated up the the exposed land -- tundra, then conifers, then the cold rainforest that remained until humans -- the sea flooded in, cutting off England from the continent and Ireland from England. So England wound up with fewer plants and animals than the continent, and Ireland even less. Surprising as it sounds, rabbits and fallow deer are not native to either island -- they were brought by Normans less than a millennia ago. Red deer and roe deer made it to England, but the latter never reached Ireland. Neither, of course, did snakes.

Plants did the same: only some of the Continent's variety worked its way across the warming land before an ocean rushed in. The bluebells were one of the ones that made it.