There is much confusion regarding these two species and their relationship to each other and, if indeed, they are actually distinct species.
Primula whitei was described first, in 1911, by W.W. Smith from plants collected by J.C. White (#122) on the Pe-le La, Bhutan 27°32'50.33"N 90°12'57.39"E. The holotype is in Calcutta, CAL0000017397, with a photograph of the type at Royal Botanic Garden Edinburgh, E00024821. Many additional collections were also gathered by Ludlow & Sherriff and R.E. Cooper.
Primula bhutanica was described in 1941 by Fletcher who recognised that some plants collected under P. whitei showed consistent, distinct characteristics separate from true P. whitei. Several collections are listed in the description, but the holotype is Ludlow and Sherriff #1166 from the Choling La, in Eastern Bhutan 27°19'22.59"N 91°46'33.69"E and resides at Royal Botanic Garden Edinburgh E00024661.
The distinct characteristics used to separate the two species are: the calyx lobes which are entire (undivided) in P. bhutanica and fimbriated (fringed) in P. whitei, and the corolla lobes which are tridentate (three toothed) in P. bhutanica and crenulate (finely wavy) in P. whitei. Both species are blue with a white zone in the center and a yellowish-green eye. The distribution of the two species is split with P. bhutanica occurring further east than P. whitei.
|Characteristics of P. bhutanica|
|Characteristics of P. whitei (courtesy RBGE)|
In 1947, L&Ss&E observed and collected under #12299 near Tongkyuk Dzong in Tibet 29°57'39.88"N 94°46'49.59"E a population of plants that had characteristics of both species - some plants had tridentate petals and others had finely crenulately toothed petals. They stated in the field notes: "Specimens under this number should not be separated. All specimens were collected in one spot and represent one species."
|From John Richards (Spring leaf left, Fall leaf right)|
So only further observations of plants in the wild will help solve this problem.
The Flora of Bhutan keeps the two species distinct but notes that P. bhutanica may only warrant subspecies status within P. whitei.
The Flora of China (1994) reduces P. bhutanica to a synonym of P. whitei with the explanation given in the Chinese version stating that from observations in the wild and the Ludlow & Sherriff collections 12299 and 12291 show the distinction between the corolla lobes and calyx used to separate the two species is mixed in that population.