<i>Lithothamnion</i> (Hapalidiales, Rhodophyta) in the changing Arctic and Subarctic: DNA sequencing of type and recent specimens provides a systematics foundation*

Coralline red algae in the non-geniculate genera Clathromorphum, Phymatolithon and Lithothamnion are important benthic ecosystem engineers photic zone of Arctic Subarctic. In these regions, systematics biogeography Clathromorphum have mostly been resolved whereas has not, until now. Seventy-three specific infraspecific names were given to Subarctic specimens late 19th early 20th century by Frans R. Kjellman Mikael H. Foslie. DNA sequences from 36 type specimens, five historical an extensive sampling recent collections resulted recognition four species, L. glaciale, lemoineae, soriferum tophiforme. Three genes sequenced, two plastid-encoded, rbcL psbA, mitochondrial encoded COI-5P; COI-5P segregated glaciale tophiforme but psbA did not. Partial obtained enabled us correctly apply earliest available place remainder synonymy. We unable sequence another 22 all more than those that now applied. It is difficult identify species solely on morpho-anatomy as they can occur encrusting corallines or maerl (rhodoliths). demonstrate importance sequencing showing recently proposed North-east Atlantic erinaceum a synonym one published Lithothamnion, soriferum, itself incorrectly placed synonymy under based morpho-anatomy. Based sequenced we update distributions ecology species.