Primroses and cowslips have a habit of spontaneously producing odd forms called sports, which are often very appealing. There are various sports of P. vulgaris  that expand the range of suitable primroses for American woodland gardens. The most desirable form resulting from genetic whim is the so-called hose-in-hose primrose, which has been prized as a garden plant for centuries. Flower clusters are made up of layered blossoms, one tucked inside the tube of another.

-Sydney Eddison, It’s primrose time, Fine Gardening issue #172