Purshia species form deciduous or evergreenshrubs, typically reaching 0.3–5 metres (1–16+1⁄2 feet) tall. The leaves are 1–3 centimetres (1⁄2–1+1⁄4 inches) long, deeply three- to five-lobed, with revolute margins. The flowers are 1–2 cm in diameter, with five white to pale yellow or pink petals and yellow stamens. The fruit is a cluster of dry, slender, leathery achenes which are 2–6 cm long. The roots have nodules that host nitrogen-fixingFrankia bacterium.[1]
Taxonomy
Taxonomic history
The genus was originally placed in the subfamily Rosoideae.[2] In the past, the evergreen species were treated separately in the genus Cowania; this genus is still accepted by some botanists.
Modern classification
The classification of Purshia within the family Rosaceae has been unclear.[3][4] It is now placed in the subfamily Dryadoideae.[2]
^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 (1–2): 185–192. doi:10.1023/A:1004240004063.
^ abPotter, D.; Eriksson, T.; Evans, R.C.; Oh, S.; Smedmark, J.E.E.; Morgan, D.R.; Kerr, M.; Robertson, K.R.; Arsenault, M.; Dickinson, T.A.; Campbell, C.S. (2007). "Phylogeny and classification of Rosaceae". Plant Systematics and Evolution. 266 (1–2): 5–43. Bibcode:2007PSyEv.266....5P. doi:10.1007/s00606-007-0539-9.
^Morgan, D.R.; Soltis, D.E.; Robertson, K.R. (1994). "Systematic and evolutionary implications of rbcL sequence variation in Rosaceae". American Journal of Botany. 81 (7): 890–903. doi:10.1002/j.1537-2197.1994.tb15570.x. JSTOR2445770.
^Eriksson, T.; Hibbs, M.S.; Yoder, A.D.; Delwiche, C.F.; Donoghue, M.J. (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): 197–211. doi:10.1086/346163.
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