The narrow endemic Sphagnum troendelagicum is an allopolyploid derivative of the widespread S-balticum and S-tenellum

Sphagnum troendelagicum is only known from five localities in central Norwa y. Three populations were analyzed to assess its genetic affinities with ot her Sphagnum species. Isozyme and cytological data indicate that the specie s is allopolyploid. Morphological, RAPD, and isozyme data further indicate that it has originated from hybridization between Sphagnum tenellum (sect. Mollusca) and S. balticum (sect. Cuspidata). Sphagnum troendelagicum is mor phologically distinct, with unique combinations of character states found i n sect. Cuspidata and sect. Mollusca. Sphagnum tenellum is genetically simi lar to S, balticum, although these species are morphologically divergent. O ur data support the inclusion of S. tenellum within sect. Cuspidata. Sphagn um troendelagicum appears to have originated recurrently; thus its restrict ed distribution cannot be ascribed to a single origin. The progenitor speci es are widespread in the Northern Hemisphere and often grow sympatrically i n boreal areas. Hypotheses that may account for the restricted distribution of S. troendelagicum including ecological tolerance of the allopolyploid a nd opportunities for hybridization between the progenitors, are discussed.