| Summary: | Flower colour has played a decisive role as an evolutionary force in many groups of plants by driving speciation. A well-known example of colour polymorphism is found across the Mediterranean populations of Lysimachia arvensis and L. monelli, in which blue- A nd red-flowered plants can be found. Previous studies recognized two lineages within L. arvensis differing in flower colour, but this variation has not yet been considered in a phylogenetic context. We have reconstructed the ancestral states of flower colour across Mediterranean Lysimachia spp. aiming at understanding its phylogenetic signal using the nuclear internal transcribed spacer (ITS) sequences and three plastid markers. All blue- A nd red-flowered specimens were nested in different clades in the ITS tree, thus supporting that L. arvensis and L. monelli are polyphyletic, whereas low phylogenetic resolution was found in plastid markers. Monophyly was reconstructed for blue-flowered L. arvensis and L. monelli samples, and similarly for red-flowered individuals of each species: (1) blue-flowered L. arvensis was reconstructed as sister to the strictly blue-flowered L. talaverae in a monophyletic clade sister to remaining Lysimachia; (2) red-flowered L. arvensis was resolved as sister to red-flowered L. monelli in a monophyletic clade; and (3) clade 2 was sister to blue-flowered L. monelli and the strictly blue-flowered L. foemina. Our results suggest that colour lineages in L. arvensis and L. monelli constitute different species, but flower colour did not promote the separation of these lineages. We propose a new name for blue-flowered L. arvensis (L. loeflingii) and a new combination for red-flowered L. monelli (L. collina), maintaining L. arvensis for red-flowered plants and L. monelli for blue-flowered plants. © 2022 The Linnean Society of London.
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