Abstract
Porella obtusata is a liverwort with a southwestern distribution in Europe. In Norway it is confined to areas with oceanic climate along the west coast, where it also reaches its northern limit. Typically it is growing on sunlit, base rich rocks at sea level in southwestern Norway, a scarce habitat in these coasts dominated by granitic bedrock. There are some old records, but investigations after year 2000 have yielded much new information. Porella obtusata is a rare species in Norway, and the new information shows that its habitat is threatened by exploitation and shrub encroachment of the shoreline.
Highlights
The liverwort Porella obtusata (Tayl.) Trev. has status as a threatened species in Norway, and is evaluated as endangered (EN) in the Norwegian red list (Hassel et al 2010)
Porella obtusata has for a long time been known from Kvitsøy County, and here it is recorded from many localities
The Norwegian distribution of Porella obtusata is confined to the southwestern coast, an area which is characterized by an oceanic climate with mild winters and cool summers (Størmer 1969)
Summary
The liverwort Porella obtusata (Tayl.) Trev. has status as a threatened species in Norway, and is evaluated as endangered (EN) in the Norwegian red list (Hassel et al 2010). The rarity and decline of P. obtusata in Norway does not seem to result from natural fluctuations of populations at the edge of their distribution. M.X.Zhang has proven not to be conspecific with the European P. obtusata (Hentschel et al 2007), and is better treated as Porella macroloba (Steph.) S.Hatt. The wide Mediterranean distribution of P. obtusata may indicate survival during the last glacial maximum in several refugial areas like Asia Minor, Italy, Spain, and one or more of the Macaronesian Islands (Taberlet et al 1998, Ansell et al 2011, Hutsemékers et al 2011). Based on current distribution the source populations for northward dispersal after the last glaciation were most likely situated on the southwestern European mainland or Macaronesia (Kyrkjeeide et al 2014). Few records have been added after Jørgensen (1934) until the year 2000, but thereafter the species has been searched for more systematically, especially in the period 2008–2015
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