Dryas (plant)
White Mountain Avens ( Dryas octopetala )
The silver Wurzen ( Dryas ) are a genus of flowering plants of the rose family ( Rosaceae ) with distribution in tundra and two alpine species in the northern hemisphere.
Description
Silver Wurzen are creeping branched, evergreen, woody dwarf shrubs. The close-set against ever- arranged leaves are deeply cut at the edge, as a rule, rarely entire. Stipules are present.
The achselbürtigen, showy single flowers are long-stalked and hermaphrodite or reduced to a gender. The flower cup is cup- to cup-shaped. The seven to ten sepals are dachziegelig to klappig, their number is always the same as that of the white, off-white or yellow petals. Stamens and pistils are numerous, the latter are non- growing on the base of the flower cup. The Stylodien are hairy terminally and long. The tiny, linealischen scars are terminal and longitudinally furrowed.
The fruits are achenes, which end in the not frail, elongated and hairy Stylodia. There is only one ovule. The seeds have a membranous surface. The chromosome number is 2n = 18
Dissemination
The genus occurs in tundra and alpine regions of the northern hemisphere. While the White Mountain Avens occurs circumpolar ( in Central Europe ), Dryas drummondii limited to Northeast Asia and North America.
The detectable in sandy clay deposits fossil deposits (especially Dryas octopetala L. ) from the cold periods show a wide distribution of the silver Wurzen in the glacier -free north-western tundra vegetation of Europe, which namesake was the Dryas - floras of the Würm glaciation, especially the younger Dryas.
System
The genus Dryas was erected in 1753 by Carl Linnaeus. Together with the genera Cercocarpus, Chamaebatia and Purshia it forms the subfamily Dryadoideae within the family Rosaceae.
Depending on the author, the genus Dryas contains two to six types:
- White Mountain Avens ( Dryas octopetala L.)
- Yellow Avens ( Dryas drummondii Richards. )
- Dryas alaskensis AEPorsild ( Syn: Dryas octopetala subsp alaskensis ( AEPorsild ) Hultén. )
- Dryas crenulata Juz.
- Dryas hookeriana Juz.
- Dryas integrifolia M.Vahl