What is "cushion plant"

A cushion plant is a compact, low growing, mat forming plant that is found in alpine, subalpine, arctic, or subarctic environments around the world. The term "cushion" is usually applied to woody plants that grow as spreading mats, are limited in height above the ground (a few inches at most), have relatively large and deep tap roots, and have life histories adapted to slow growth in a nutrient poor environment with delayed reproductivity and reproductive cycle adaptations. The plant form is an example of parallel or convergent evolution with species from many different plant families on different continents converging on the same evolutionary adaptations to endure the harsh environmental conditions.