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 Central Nepal. 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. However, the toothing may vary so this should not be used as the sole characteristic to determine an identification. Often produces 4 petals instead of the normal 5. It 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.