Plant 282

Dryas octopetala L. (Rosaceae)

Mountain avens

Dryas octopetala is an attractive, creeping, dwarf evergreen shrub. It has erect, solitary, white flowers resembling little saucers, and leaves that often form dense mats over limestone rocks. Unusually for a species in the rose family, individual flowers have eight petals (hence the specific name), sometimes ten; the more usual number for the family is five. There are plentiful yellow stamens and carpels at the flower's centre. As the sun moves, so the flowers slowly turn to face it. This action is thought to increase their temperature, and make them attractive to flies that act as pollinators. The leaves are dark green and wrinkled above, with scalloped margins; underneath they are covered with dense, white hairs. Fruit have long, persistent feathery styles that aid wind dispersal. Cultivation of the plant is easily achieved in a sunny position, and is very suitable for a rock garden or wall, or as groundcover. The plants are resistant to frost. In natural habitats, plants can live for more than 100 years.

Dryas octopetala has a circumpolar distribution being native in the Arctic, sub-Arctic and alpine regions. It occurs in Greenland, Iceland, Scandinavia, Canada, western North America and in the mountainous areas of Europe, especially the Alps and as far south as central Italy. It is very rare in England and Wales but is found at sea-level on shell-sand in northern Scotland and on limestone pavement in Ireland. It is the national flower of Iceland.

The coralloid roots of Dryas species in Alaska and Canada form associations with symbiotic, nitrogen-fixing bacteria in the genus Frankia. Soil fungi also form mycorrhizal associations with the roots of Dryas species.

Two geological periods of cool climatic temperatures are named after the plant, the 'Younger Dryas' and the 'Older Dryas'. These periods have occurred since the Last Glacial Maximum was on the decline about 20,000 BP. Dryas octopetala became common in Europe during these cooler periods, and is thought to have been one of the main species of open tundra communities. Fragments of its leaves have been found in lake sediments, sometimes in abundance, in Scandinavia, from the late-glacial. Dryas pollen also occurs in these deposits.

Fossil records show that the species was present in southern Britain but became extinct in the region when closed forest became the dominant vegetation. Although long-lived, today the plant's survival is threated by overgrazing, particularly from rabbits and, in the Arctic, from reindeers.

Further reading

Elkington TT 1971. Dryas octopetala L. Journal of Ecology 59: 887-905.

Walker KJ 2015. Dryas octopetala L., mountain avens. Species account. Botanical Society of Britain and Ireland.

Serena Marner