P. strumosa or P. calderiana subsp. strumosa ?

 

Primula strumosa

The yellow flowered species, P. strumosa was described from plants found at Champa Pumthang in Bhutan and it was associated with P. elongata  which it distinguished in having a long seed capsule opening by valves. The purple flowered species, P. calderiana, was described from plants found near Changu in Eastern Sikkim. It had been confused with an earlier described species, P. obtusifolia, a nivalid, from which it is easily distinguished by the leaves and seed capsule.

Primula calderiana

P. calderiana and P. strumosa are very similar in their characteristics but differ in flower color, and perhaps scent (this is very subjective) and in their geographical ranges, with P. calderiana distributed in the Eastern part of the Himalayas and P. strumosa distributed to the West. These two species rarely meet, but when they do, hybridization occurs, giving a range of muddy colors.

Primula calderiana X  Primula strumosa

John Richards in Journal of the Scottish Rock Garden Club 15(3):211. 1977. acknowledges that the range of the two species are mostly separate but notes that wild hybrids do occur. His testing of cultivated hybrids shows that they are 100% pollen-fertile. Therefore, he placed P. strumosa as a subspecies of P. calderiana. Often the criteria used to describe a subspecies is if it is capable of interbreeding and producing fertile offspring with the species in the wild, but does not interbreed due to factors such as geographic isolation, etc.

Subsequent to Richards publication, Polunin & Stainton in "Flowers of the Himalaya" (1984) and Gould in Hara, An enumeration of the flowering plants of Nepal" (1982) followed Richards without comment. The Flora of Bhutan (1999) and The Flora of China (1994) retained P. strumosa as a distinct species with comments justifying their positions. Mostly, this is based on notes by Ludlow that in the field, pure P. strumosa was found at a higher elevation than pure P. calderiana and the only hybrids were found at an intermediate elevation between the two pure populations. The recent book The Genus Primula L. in India goes one step further than Richards, in reducing P. strumosa to a variety of P. calderiana but they do not justify this position and do not acknowledge the altitudinal preferences of the two species.

Unless there is more convincing evidence, I am retaining P. strumosa as a distinct species.