Population status and ecology of the liverwort Biantheridion undulifolium (Nees) Konstant. & Vilnet in England and Wales

ABSTRACT Introduction Biantheridion undulifolium (Nees) Konstant. & Vilnet [Jamesoniella undulifolia (Nees) Müll.Frib.] is a globally rare liverwort threatened with extinction. This study was carried out to investigate its population status and ecology in England and Wales, UK. Methods Surveys were undertaken at all previously known sites where the species may currently occur in England and Wales. Geographical coordinates of colonies were recorded with a GPS unit, and counts made of occupied 1 m grid cells. Habitat and community composition were recorded by relevés. Key results Biantheridion undulifolium has been reported from 16 sites in England and Wales. It has become extinct at six (38%), and its continued existence at two others is uncertain. Following 52 h of search effort, 88 occupied 1 m grid cells were found across eight sites. The estimated true total is 196–433 occupied 1 m grid cells. Only three sites support sizeable populations; most sites support < 10 occupied 1 m grid cells. The species is confined to mesotrophic flushes and bogs, mostly occurring on hummocks of Sphagnum capillifolium s.l. that are moderately to heavily compacted by grazing livestock. Occupied hummocks tend to be composed of Sphagnum in good health, with few signs of necrosis. Fertile plants of this dioicous liverwort are rare, and no sporophytes were found. Conclusions Biantheridion undulifolium is a ‘competitive perennial stayer’ with limited dispersal ability, and has undergone a significant decline in England, and probably also in Wales. Adequate grazing pressure appears to be especially important for its survival. Most sites occur outside protected areas.