1. An organism living above or beyond the tree line and frequently in areas of heavy snow.
2. A plant with a requirement for a temperature of less than 10ºC in the warmest month, typically occurring in regions with a mean annual temperature below 0ºC; sometimes used to refer to those organisms living above the tree line in areas of heavy snow.
3. A plant that can grow in very cold environments, as the arctic and antarctic lichens and mosses.