Dryas (plant)


Dryas is a genus of perennial cushion-forming evergreen dwarf shrubs in the family Rosaceae, native to the arctic and alpine regions of Europe, Asia and North America. The genus is named after the dryads, the tree nymphs of ancient Greek mythology. The classification of Dryas within the Rosaceae has been unclear. The genus was formerly placed in the subfamily Rosoideae, but is now placed in subfamily Dryadoideae.
The species are superficially similar to Geum, Potentilla and Fragaria. However, Dryas are distinct in having flowers with eight petals, instead of the five petals found in most other genera in the Rosaceae. The flowers are erect and white with a yellow centre or pendulous and all-yellow, and held conspicuously above the small plants. This makes them very popular in rockeries and alpine gardens. The hybrid Dryas × suendermannii, with cream coloured flowers, has gained the Royal Horticultural Society’s Award of Garden Merit.
Dryas tolerates a wide variety of unshaded habitats, including alpine situations with sand or gravel substrate, similar substrates in flat tundra lowlands, and also fen habitats upon organic substrate where some shading from adjacent sedges or shrubs may occur.
The Younger Dryas and Older Dryas stadials are geological periods of cold temperature that are named after Dryas octopetala, which flourished during that time and is used as a fossil indicator of those periods.

Species

Dryas comprises three species, but the genus is in need of taxonomic revision:
Two hybrids have been described:
Some Dryas plants have root nodules that host the nitrogen-fixing bacterium Frankia.