Dryas octopetala

Dryas octopetala
File:Dryas octopetala LC0327.jpg
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Rosales
Family:	Rosaceae
Genus:	Dryas
Species:	D. octopetala
Binomial name
Dryas octopetala L.

Dryas octopetala (common names include mountain avens, eightpetal 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. 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.

Distribution

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, Iceland, 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 is found in Alaska, most frequently on previously glaciated terrain, reaching as far south as Colorado in the Rocky Mountains.

As a floral emblem, it is the official territorial flower of the Northwest Territories and the national flower of Iceland.

Description

The stems are woody, tortuous, with short, horizontal rooting branches. The leaves are glabrous above, densely white-tomentose beneath. The flowers are produced on stalks 3–10 cm (1.2–3.9 in) long, and have eight creamy white petals - hence the specific epithet octopetala. The style is persistent on the fruit with white feathery hairs, functioning as a wind-dispersal agent. The feathery hairs of the seed 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, Older Dryas and Oldest 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.

Cultivation

D. octopetala is cultivated in temperate regions as groundcover, or as an alpine or rock garden plant. It has gained the Royal Horticultural Society's Award of Garden Merit. The leaves are occasionally used as a herbal tea.

Gallery

• Weiße Silberwurz (Dryas octopetala) 2.jpg
• Dryas octopetala Liechtenstein.jpg
• Dryas octopetala a4.jpg
• Dryas octopetala seed head.jpg

  Seed head of Dryas octopetala

• Weiße Silberwurz (Dryas octopetala) 1.jpg