Winter Heather is a plant for Plants Against Humanity, she's a non-attacking plant that affects every zombie that walks onto the tile she's on. She is unlocked after beating 1-8. Her main use is to slow down zombies and put out Fire Zombies from burning plants.
Winter Heather is based off the real life plant with the same name, though designed somewhat differently, with icicles coming from the root, with flowers coming out. The "Winter" in her name is in reference to her ability to freeze a tile.
Winter Heather makes for an effective early-game defense that can still be useful later on by slowing down zombies to give other plants more time to attack, or lets Potato Mine have more time to arm itself, or to gain more sun to plant stronger units. That being said, it's usefulness in Survival levels are a bit more questionable, as Winter Melon makes it's ability obsolete. Winter Heather's also not very effective with fire plants, as they render it's ability useless.