Primroses bear two distinct forms of flower. In “pin-eyed” blooms, the stigma is held above the anthers; in “thrum‑eyed” flowers, it sits lower – an arrangement that promotes cross-pollination. Charles Darwin was intrigued by this dimorphism and demonstrated that crossing the two forms yields significantly more seed. The plants hybridise readily with related garden primulas, creating a gentle spectrum of colour, from pure white through blush pink to deep magenta.