Up until recently the highest chromosome number known in roses was octoploid (2n=8x=56). C.C. Hurst had hypothesised that all roses derive from a theoretical Arctic decaploid (2n=10x=70), from which he theorised all other roses descend by progressive loss of chromosome complements. This decaploid was never found.
However, it is now established that a rose found on the Zhongdian Plateau of China is decaploid. This high plateau (over 3000m elevation) in Yunnan is the gateway to the Tibetan plateau. It has a stunningly rich flora, although the natural ecosystems have been severely damaged by yak and cattle overgrazing.
On this plateau grows the decaploid Rosa praelucens, the Shangri-La Rose, an elegant rose with large solitary pink to red flowers and leaves with small hairy leaflets.
Is this the ancestral decaploid of Hurst? No, Hursts theory is still wrong. Instead of having chromosomes of all five of Hurst's fundamental rose types (his "septets") it appears to be a specialised Chinese rose, possibly sharing a hybrid origin with Rosa roxburghii, the Chestnut Rose, which it slightly resembles. The Flora of China classifies both the Chestnut Rose and the Shangri-La Rose in section Microphyllae as they both have a depressed-globose hypanthium with achenes inserted at projecting torus at the base.
See: Jian, H. et al. (2010). Decaploidy in Rosa praelucens Byhouwer (Rosaceae) Endemic to Zhongdian Plateau, Yunnan, China. Caryologia 63: 162-167.
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