Bog carnivorous plants evolved to capture nitrogen their roots cannot obtain

Evidence

Bogs are the exclusive homes for insectivorous plants like sundews, pitcher plants, and Venus’ fly traps which perch on the Sphagnum mat. Deer flies and mosquitoes are plentiful in a bog and each one is a flying packet of concentrated animal nitrogen. The sticky traps and elaborate pitchers evolved to capture this nitrogen for the plant, gaining by carnivorous leaves what its roots could not provide. — Robin Wall Kimmerer, Gathering Moss, 459