Silene alba and S. dioica in North America and the generic delimitation of Lychnis, Melandrium, and Silene (Caryophyllaceae)
Evidence is presented from numerical studies of herbarium and cultivated specimens and from observations on time of flowering that North American weed populations of white cockle are referable to the European Silene alba (≡ Lychnis alba ≡ Melandrium album) and are not, as has been suggested, the products of hybridization between that species and S. dioica. The present status and distribution in North America of S. alba, S. dioica, and the hybrids between them are described. Evidence for different generic circumscriptions of Silene, Lychnis, and Melandrium is analysed and the limited applicability of the capsule dehiscence character is demonstrated. Recent treatments that accept Lychnis in a narrow sense and assign most of the North American species of the group to a large genus Silene are accepted pending further study. Two new subspecific combinations (S. uralensis subsp. attenuata (Farr) McNeill and S. uralensis subsp. montana (S. Watson) McNeill) are proposed.