Tasmanian cushion plants are low growing, highly compact, woody, spreading mats that can grow up to 3 m in diameter, located mainly on the island of Tasmania. These mats are made up of tightly packed stems that grow at the same rate so that no apical rosettes protrude above the rest. The term cushion plant refers to a characteristic growth habit adopted by various species from a range of families to adapt to alpine and subalpine environments and areas of high latitude. They are adapted to grow in low nutrient areas and typically have deep taproots. Cushion plants are very slow growing and do not grow high above ground; mounds typically remain under 30 cm high. Underneath the living surface of the cushion, the plants either allow dead leaves to persist or produce non-photosynthetic material, resulting in an insulating effect. Floristics of Tasmanian cushion plant community Six families, including seven species, of cushion plants occur in Tasmania, and one additional family and species occur on Macquarie Island. Three additional families, including seven species, can adapt to the bolster habit, although not exclusively. The cushion plant growth habit is linked with drainage and the plant's ability to redirect water flow due to its growth pattern. Evolution The cushion plant is an example of convergent evolution. Unrelated species from a number of different families on separate continents have evolved the cushion form to adapt to similarly harsh environments. Ecosystem function Cushion plants have been shown to be a keystone species in the ecosystem in which they occur. For example, Azorella macquariensis is the only cushion-forming plant that occurs on Macquarie Island and it plays a vital role in the ecosystem as it makes up the major structural component of feldmark vegetation on the island. Cushion plants are also often considered "nurse species", as their presence is necessary in order for many other alpine species to become established. Cushion plants have been found to enhance species richness in areas with inherent impoverished local diversity. This effect is due to their low and compact growth form that alleviates severe alpine conditions. Several Tasmanian cushion species have been found to have a surface temperature up to 10 °C greater than the ambient temperatures. The warmer temperatures allow the plants to continue to photosynthesize and grow in conditions that would otherwise inhibit such productivity. This substantially extends the growing season. In addition, a combination of the