Plagiochila britannica,a new species in the British Isles

Abstract

Plagiochila britannica is described as a new species. It differs from P. porelloides and P. asplenioides in many characters, especially its often more narrowly oval leaves with a more variable, often truncate to bilobed apex and larger cells, its wider antical stem cells and its diploid chromosome number. Differences from P. arctica var intermedia include its more variable leaf apex, generally more dentate leaves often with longer teeth, the greater maximum size of its leaf cells and its wider antical stem cells. Male and female inflorescences and sporophytes are known in P. britannica, which favours base-rich substrata and has been found in Wales, N. England, Scotland and N. Ireland. A key to the nine species of Plagiochila in the British Isles is included.