Contribution à la connaissance de quelques Characées du Nord de la France

Abstract

Abstract Survey of the hydrophytic flora of small stretches of water in northern France has allowed the observation of several taxa of the Characeae family here reported, namely Chara vulgaris, Chara vulgaris f. longibracteata, Chara globularis, Chara curta, Nitella gracilis and Tolypella glomerata. According to current literature, 25 taxa within Characeae are present in northern France, at species, variety or form level. Chara vulgaris, as a complex, is very frequently found in northern France in newly created stretches of water. It colonizes meso-eutrophic waters and shows a cosmopolitan distribution. The type species seems to be rarer locally than the longibracteata form, but more investigations are needed to confirm this observation. Chara globularis has been recorded on the coastline of northern France, in the peat bogs at the back of the coastline, in the humid dune slacks and further inland where the plant can survive winter, in some mining slag ponds in the area of Valenciennes, the water of which has been qualified as sub-briny. Nitella gracilis in the area is perceived as a meso-eutrophic to oligo-mesotrophic water species, although in Brittany and Germany its presence has been noted in acidophilous communities together with Potamogeton polygonifolius, Littorella uniflora or Sphagnum spp. The species is mostly present in western France, and is very rare in eastern France. Tolypella glomerata has been very rarely observed in northern France. The observation here reported in a small pond on the hill of Marchenelles is only the third report in the area. The species is not expressed there as a monospecific community (as usually reported) and must be searched for within a very dense Chara vulgaris var. longibreactata cover that develops in early spring. To facilitate the identification of these plants in the field, an illustrated description of each taxa identified has been provided.