Discussion of the challenges associated with recognising infra-specific variation in a hierarchical system of classification, illustrated using two colour forms of Lathraea clandestina

Abstract The approximate date of introduction to the British Isles of Lathraea clandestina L. is clarified and forma names provided for white and pink-flowered variants of the species. The use of forma names to recognise single-character variants is examined and found to be inherently contradictory to hierarchical classification. An extension of the Group system employed for cultivated plants to plants occurring in the wild is advocated.