| Dryas octopetala | ||||||||||||||
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| Dryas octopetala L. | ||||||||||||||
Dryas octopetala (common names include mountain avens, white dryas, and white dryad) is an arctic-alpine flowering plant in the family Rosaceae. It is a small prostrate evergreen subshrub forming large colonies, and is a popular flower in rock gardens. The specific epithet octopetala derives from the Greek octo (eight) and petalon (petal), referring to the eight petals of the flower, an unusual number in the Rosaceae, where five is the normal number. However flowers with up to 16 petals also occur naturally.
Dryas octopetala has a widespread occurrence throughout mountainous areas where it is generally restricted to limestone outcrops. These include the entire Arctic, as well as the mountains of Scandinavia, the Alps, Carpathian Mountains, Balkans, Caucasus and in isolated locations elsewhere. In Great Britain, it occurs in the Pennines (northern England), at two locations in Snowdonia (north Wales), and more widely in the Scottish Highlands; in Ireland it occurs on The Burren and a few other sites. In North America, it reaches as far south as Colorado in the Rocky Mountains.
The stems are woody, tortuose, with short, horizontal rooting branches. The leaves are glabrous above, densely white-tomentose beneath. The flowers are produced on stalks 3-10 cm long, and have eight creamy white petals. The style is persistent on the fruit with white feathery hairs, functioning as a wind-dispersal agent. The feathery hairs of the sea head first appear twisted together and glossy before spreading out to an expanded ball which the wind quickly disperses.
It grows in dry localities where snow melts early, on gravel and rocky barrens, forming a distinct heath community on calcareous soils.
Climatology
The Younger Dryas and Older Dryas stadials are named after Dryas octopetala, because of the great quantities of its pollen found in cores dating from those times. During these cold spells, Dryas octopetala was much more widely distributed than it is today, as large parts of the northern hemisphere that are now covered by forests were replaced in the cold periods by tundra.
