Perennial of the Primulaceae family, this cultivar belongs to the Primula marginata group, a species endemic to the Franco-Italian Maritime Alps, where it inhabits the cliffs and crevices of limestone rocks between approximately 1,000 and 2,500 meters in altitude. 'Sheila Denby' is a named cultivar present in the collections of specialized rock gardeners, although its selection history is not documented with certainty in the sources consulted.
This cultivar is immediately distinguished by its distinctly dark and shiny green foliage, with a very discreet farina, limited to a fine white border on the toothed margins. This characteristic clearly differentiates it from most other marginata cultivars, whose foliage is usually gray-glaucous to heavily farinose. The leaves are oval to spatulate, leathery, with well-marked dentition.
The flowers are a soft lilac to pale violet, borne on slender stems in sparsely dense umbels. The corollas have well-cut, notched petals, with an elongated tube clearly visible before full anthesis. The central eye, farinose and light, is characteristic of the species. In its natural habitat, the species' flowering extends from April to June depending on altitude; in cultivation, this cultivar generally blooms in March-April.
It requires rigorous drainage, a slightly calcareous mineral substrate, and protection against stagnant moisture in winter, in rock gardens or under shelter.