Dryas (plant)

Dryas
Dryas × suendermannii
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Rosales
Family:	Rosaceae
Subfamily:	Dryadoideae
Genus:	Dryas L.
Speciea
See text

Dryas is a genus of dwarf perennial herbaceous plants in the rose family Rosaceae, native to the arctic and alpine regions of Europe, Asia and North America. The genus is named after the Greek nymph Dryas. The classification of Dryas within the Rosaceae has been unclear.^[1][2] The genus was formerly placed in the subfamily Rosoideae, but is now placed in subfamily Dryadoideae.^[3]

There are three species and one hybrid:

• Dryas drummondii – Drummond's Avens
• Dryas integrifolia – Entire-leaved Avens
• Dryas octopetala – Mountain Avens
• Dryas × suendermannii – D. drummondii × D. octopetala

The species are superficially similar to Geum, Potentilla and Fragaria, but are distinct in having flowers with eight petals (rarely seven or up to ten), instead of the five petals found in most other genera in the Rosaceae. The flowers are erect and white with a yellow centre (Dryas integrifolia, Dryas octopetala) or pendulous and all-yellow (Dryas drummondii), and held conspicuously above the small plants. The hybrid has pale yellow flowers. This makes them very popular in rockeries and alpine gardens.

Some Dryas plants have root nodules that host the nitrogen-fixing bacterium Frankia.^{[4] [5]}

Dryas is the clan badge of Clan MacNeil of Scotland.

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.

References

1. ^ Morgan, D.R., et al. (1994). Systematic and evolutionary implications of rbcL sequence variation in Rosaceae. American Journal of Botany. 81(7): 890–903.
2. ^ Eriksson, Torsten et al. (2003), "The Phylogeny of Rosoideae (Rosaceae) Based on Sequences of the Internal Transcribed Spacers (ITS) of Nuclear Ribosomal DNA and the trnL/F Region of Chloroplast DNA", International Journal of Plant Sciences 164 (2): 197, doi:10.1086/346163, http://www.biology.duke.edu/yoderlab/reprints/2003Eriksson_et_alIJPS.pdf 
3. ^ Potter, D., et al. (2007). Phylogeny and classification of Rosaceae. Plant Systematics and Evolution. 266(1–2): 5–43.
4. ^ Swensen, S.M.; Mullin, B.C. (1997). The impact of molecular systematics on hypotheses for the evolution of root nodule symbioses and implications for expanding symbioses to new host plant genera. Plant and Soil. 194: 185–192.
5. ^ Markham, J. H. (2009). Does Dryas integrifolia fix nitrogen? Botany. 87: 1106-1109.

• Germplasm Resources Information Network: Dryas
• Huxley, A. (1992). New RHS Dictionary of Gardening. Macmillan [D. × suendermannii].