A little known species, found in 1920 on the Shing Hong, Burma (Myanmar) - China border region. The flower is similar to P. morsheadiana (P. prenantha ssp. morsheadiana) and to P. serratifolia var. unicolor, which grow in the same general area but the leaves are distinct being oblanceolate and acute and shortly apiculate at the apex. The margin also differs from the other two species in being regularly dentate (versus iregularly dentate). The collector, Farrer, commented on his specimens having one whorl, but being young plants, he suggested that the species may have several whorls which is the case in the images below.
In 1937 and 1938, T.T.Yu made collections identified as this species in the upper Chiukiang (Dulong jiang) Valley (19708) and the Salween-Chiukiang divide (19313). Collection 19708 seems to be of P. prenantha and I have not seen an example of collection 19313. The Yu collections may be the reason for the Chen reference (which I have not seen) being auct. non. W.W.Sm. John Richards reduced this species to a synonym of P. prenantha based on some of the very limited specimens having leaves with apex both acute and rounded.