Understanding Primula odontocalyx

In the Spring 2015 AGS/SRGC show at Kendal, a plant was shown as “Primula aff. odontocalyx” and this has resulted in discussion over whether this is Primula odontocalyx or not.

P. aff odontocalyx: courtesy David Rankin
Primula odontocalyx was first described as a variety of P. petiolaris in 1895, but was then elevated to species status by Pax in 1905. The species was based on Farges971 collected near Tchen-kéou-tin (now Chengkou  county, NE Sichuan). The plant in question came from Wushan county, just south of Chengkou so the location is a good match. The Flora of China gives the distribution as S Gansu, W Henan, W Hubei, S Shaanxi, Sichuan, but not W Yunnan (Mekong Salween divide) where apparently the BASE 9547 P. aff. odontocalyx was collected. The similar and related species P. euosma is from that area and the BASE collection may be that species.
The description of the species says that the large flowers are borne on a scape and that the calyx has 2-3 teeth on the apex. There are 3 sheets of Farges 971 in the Paris herbarium, showing 9 plants in total. Most are 2-3 flowered, but vary from single flowered to 6 flowered.  Though a key characteristic is the calyx teeth, and the species was named for this feature, not all of the type specimens show this. Some are entire and undulating. This is a discrepancy noted previously by Smith & Fletcher. The show plant is white flowered but this was a variant in a normal purple with a white eye flowered population.
The plant in question spreads vegetatively by short stolons and this feature isn’t seen on the herbarium specimens nor is it mentioned in the description of P. odontocalyx, but the material available at the time was limited and the plant was not in cultivation then.
Links to the relevant descriptions, herbarium sheets and more images are available in the species gallery under P. odontocalyx. In general it seems as though the description of the species P. odontocalyx was unfortunately difficient causing uncertainty about this species. There is no doubt in my mind that this plant in question falls within P. odontocalyx.


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