Dryas octopetala

{{Speciesbox

|image = Dryas octopetala LC0327.jpg

|genus = Dryas (plant)

|species = octopetala

|authority = L.

|range_map = Dryas octopetala distribution.svg

|range_map_caption = Global distribution

|synonyms_ref = {{cite web | url = https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:724675-1 | author=Govaerts R | website = Plants of the World Online | title = Dryas octopetala L. | publisher=Board of Trustees of the Royal Botanic Gardens, Kew | access-date = 14 December 2020}}

|synonyms =

{{Collapsible list

|title = Synonyms list

Dryadaea octopetala (L.) Kuntze
Dryas ajanensis Juz.
Dryas alaskensis Porsild
Dryas alpina Salisb.
Dryas babingtoniana A.E.Porsild
Dryas caucasica Juz.
Dryas caucasica Juz. ex Woronow
Dryas chamaedrifolia (Crantz) Gray
Dryas chamaedrifolioides Pall.
Dryas chamaedryoides Pall.
Dryas crenata Raf.
Dryas depressa (Bab.) Bab.
Dryas eriopoda Gand.
Dryas henricae auct.
Dryas hookeriana Juz.
Dryas incanescens Juz.
Dryas incisa auct.
Dryas lanata Stein ex Correvon
Dryas lepida Gand.
Dryas montana Bubani
Dryas nervosa Juz.
Dryas nivea F.Kern. ex Correvon
Dryas octopetala var. angustifolia C.L.Hitchc.
Dryas octopetala var. camschatica (Juz.) Hultén
Dryas octopetala var. depressa Bab.
Dryas octopetala f. hirsuta Hartz
Dryas octopetala var. luteola Hultén
Dryas octopetala subsp. punctata (Juz.) Hultén
Dryas octopetala subsp. subincisa Jurtzev
Dryas octopetala var. viscida Hultén
Dryas octopetala subsp. viscida (Hultén) Kozhevn.
Dryas pentaphyllaea Hill
Dryas punctata Juz.
Dryas punctata var. cinerea Jurtzev
Dryas punctata var. kamtschatica (Juz.) Kozhevn.
Dryas subincisa (Jurtzev) Tzvelev
Dryas subincisa var. minor (Hook.) Tzvelev
Dryas tschonoskii Juz.
Dryas vagans Juz.
Geum chamaedrifolium Crantz
Geum octopetalum (L.) E.H.L.Krause
Ptilotum octopetalum (L.) Dulac

}}

Dryas octopetala, the mountain avens,{{BSBI 2007 |access-date=2014-10-17}} eightpetal mountain-avens, white dryas or white dryad,{{Grin}} 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 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.

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 {{convert|3|-|10|cm|in|frac=2|abbr=on}} long, and have eight creamy white petals – hence the specific epithet octopetala.{{cite book|last=Harrison|first=Lorraine|title=RHS Latin for gardeners|year=2012|publisher=Mitchell Beazley|location=United Kingdom|isbn=9781845337315|pages=224}} 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.

Distribution and habitat

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, the Carpathian Mountains, the Balkans, the Caucasus, and in isolated locations elsewhere. In Great Britain, it occurs in the Pennines of Northern England, at two locations in the Snowdonia region of 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, and through the Canadian Rockies{{cite web|url=http://www.plantsofcanada.info.gc.ca/taxa.php?lang=e&gid=1001748|title=Plants of Canada Database - Dryas octopetala|publisher=Government of Canada|access-date=21 February 2016|url-status=dead|archive-url=https://web.archive.org/web/20160307180350/http://www.plantsofcanada.info.gc.ca/taxa.php?lang=e&gid=1001748|archive-date=7 March 2016}} reaching as far south as Colorado in the Rocky Mountains.

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.{{cite web|title=Dryas octopetala|url=https://www.rhs.org.uk/Plants/6152/Dryas-octopetala/Details|publisher=Royal Horticultural Society|access-date=16 February 2020}}{{cite web | url= https://www.rhs.org.uk/plants/pdfs/agm-lists/agm-ornamentals.pdf | title = AGM Plants - Ornamental | date = July 2017 | page = 33 | publisher = Royal Horticultural Society | access-date = 6 February 2018}} The leaves are occasionally used as an herbal tea.

Gallery

Image:Weiße Silberwurz (Dryas octopetala) 2.jpg

Image:Dryas octopetala seed head.jpg|Seed head

Image:Weiße Silberwurz (Dryas octopetala) 1.jpg