Plague blossom (also called num’chadran and failure flowers) is an engineered plant designed by The Raven King’s real name. Bran’s grandfather, he’s an incredibly dangerous creature, and one of the few old enough to... More the See Kanon. More, A queen among her people, sometimes worshipped as a goddess, she is of the people of the Darkness, and an... More, The originator of the Unseelie Fey. More, and Faelan to try to combat the fallout from the First War, which poisoned the soil and water and air badly enough that almost all plants and crops in affected areas died.
Unfortunately, it only worked part of the way; it successfully began to draw the poison from the soil, but then something went wrong. Instead of breaking down the toxins, the plague blossoms managed to refine and condense them, creating a far more dangerous substance which dripped from their leaves.