Sphagnum beothuk new to Sweden

Sphagnum beothuk was recently found new to Europe in Norway as the dark morph of Sphagnum fuscum proved to be conspecific with the north american S. beothuk. The Norwegian distribution suggests that it may also occur in other oceanic parts of northwestern Europe. In 2016, I made a brief survey of a number of mires in the province of Bohuslän in the westernmost part of Sweden. In three bogs, I found only S. fuscum, but in one bog this species co-occurred with S. beothuk. This implies that S. fuscum is the most common of the two species in the suboceanic part of Sweden. However, to determine the actual frequency and distribution of S. beothuk, a more extensive survey of bogs in the westernmost part of Sweden is required.

The usually dark colour, the convex capitula of the shoots, and the fact that many hyalocysts lack perfect pores on the convex side in the upper third of the branch leaves, distinguish it from S. fuscum. Moreover, the branch leaves are often 5-ranked, and the stem leaves are usually less obtuse in S. beothuk than in S. fuscum. (Kyrkjeeide et al. 2015).
Sphagnum beothuk occurs in the oceanic part of the west coast of Norway, up to the province of Troms (Fig. 1). Given that some species that are common in the oceanic part of Norway, such as Scapania gracilis Lindb., Campylopus atrovirens De Not., and Hookeria lucens (Hedw.) Sm., have a few scattered occurrences also along the west coast of Sweden (Størmer 1969), it seemed likely that Sphagnum beothuk might follow the same pattern. The dark morph of S. fuscum had, however, not previously been reported from that area.
To investigate this, I visited a number of mires in the northern part of Bohuslän between 29 September and 1 October 2016. I chose this area, as the moss flora there is poorly known, except for Sotenäset, an area of 150 km 2 near the coast (Bergqvist and Blomgren 1998). Only two previous records of Sphagnum fuscum were known from this area. I revisited one on them without finding the species. I then investigated mires along a 50 km gradient from north to south. I managed to find S. fuscum in four mires, and in one of them, Torrödmossen, S. beothuk also occurred ( Fig. 1, 2). The species mainly grew in hummocks, but occasionally also on more flat ground (Fig. 4,5).
Torrödsmossen is situated 15 km inland from the coast at Grebbestad in Bohuslän, southwestern Sweden, at an altitude of ca 125 m a.s.l., in an area with an annual precipitation of 750 mm. The vegetation has been described by Hallingbäck (1978), and some characteristics are presented below. It is a western, open and slightly raised bog, which is lacks a distinct bog margin forest. The dominant species in the hummocks are Sphagnum austinii Aust. and S. rubellum Wilson. S. tenellum (Brid.) Bory is common in the hollows. S. compactum Lam. & DC., S. molle Sull., S. pulchrum (Braithw.) Warnst., and S. balticum (Russ.) C.Jens. also occur on the bog, but none of them is dominant. Vascular plants such as Erica tetralix L., Myrica gale L., Narthecium ossifragum (L.) Huds., Trichophorum caespitosum (L.) Hartm., Rhynchospora alba (L.) Wahl, R. fusca (L.) W.T. Aiton., Drosera anglica Huds. and Carex limosa L. occur on the bog expanse.
Data from Norway suggests that Sphagnum beothuk has a distribution which is similar to that of S. austinii but slightly more oceanic (Kyrkjeeide et al. 2015). The two species also frequently co-occur. Indeed, I found the two species together at the Swedish site.
This fact could be used to predict the distribution of S. beothuk in Sweden (Fig. 2). This small survey indicates that S. fuscum is much more common. But, it would be worthwhile to look for S. beothuk at least in the most oceanic part of southern Sweden, within the core area of S. austinii (Fig. 2).