Lomentaria orcadiensis is a small, creeping bright rose-red alga, which grows as flat, triangular tufts 10-50 mm tall (occasionally 80 mm), growing on short, prostrate stems, with 1-2 orders of opposite branches. This alga grows in deep, low tidepools in shaded pools on sponges and macroalgae, down to 30 m. It is native from Norway and Iceland to Spain. It was first collected in North America, in 1853, by W. H. Harvey., and has been found from the Bay of Fundy, Nova Scotia to Bogue Sound, North Carolina. Initially, it was considered native, but recent studies utilizing historical and floristic studies, rapid assessment surveys, and molecular investigations have indicated that L. orcadiensis is introduced to North America. Hull fouling is the likeliest vector for the introduction of this alga, It remains rare, with no reported impacts.