This species has a confusing taxonomic history, being closely allied and included within P. petiolaris (from 1824) until described as distinct in 1917. P. sessilis is from the Western Himalaya, just reaching into Nepal whereas P. petiolaris is from further East in Nepal and into Sikkim. The protologue includes many syntypes though none are indicated as a holotype. P. sessilis is distinguished by the corolla lobes with a central pointed tooth on the rounded apex. (P. petiolaris has corolla lobes with a tridentate or irregularly toothed apex, the teeth not being pointed). P. sessilis is efarinose, has no flower scape. Leaves are 3-13 cm (including the distinct petiole) at flowering but expand to 20cm in fruit, oblanceolate to ovate, erose-denticulate at the margin, glabrous, efarinose. Flowers, scapeless, on slender pedicels, pale mauve with a yellow eye surrounded by a white zone. Calyx tubular, conspicuously 5 angled, cut to the middle or slightly below into lanceolate , keeled lobes. Tube 3 times the length of the calyx. A white form with narrow corolla lobes exists.