During a genetic analysis of western Atlantic Wrangeliaceae J.Agardh, specimens closely related to the generitype of Lophothamnion J.Agardh fell into a clade including the generitype of the earlier described Pleonosporium Nägeli, causing us to subsume the former genus. Two new species are described, P. novae-angliae G.W.Saunders & C.W.Schneider, sp. nov. for specimens from southern New England and New York, United States, formerly identified there as P. borreri (Smith) Nägeli, and P. ricksearlesii C.W.Schneider & G.W.Saunders, sp. nov. from Bermuda. The relationship of Pleonosporium with its sister genus Spongoclonium Sonder is discussed with the transfer of Spongoclonium australicum Womersley to Pleonosporium.
Bermuda, New England, Lophothamnion, Pleonosporium, Spongoclonium, new combination, new species