Antithamnion sparsum vs. Antithamnionella floccosa

Antithamnion sparsum and Antithamnionella floccosa in Maine

There are numerous species of uniseriate* red seaweeds in Maine. Antithamnion sparsum is of particular interest because it is a recent introduction with potentially invasive characteristics. First recorded in the Northwest Atlantic in 2021, it has since been documented at multiple locations between Midcoast and Downeast Maine, as well as along the eastern shore of Nova Scotia.

Its closest and most common lookalike is Antithamnionella floccosa, a species with a wide range that includes Maine.

*Uniseriate: a chain of single cells attached end-to-end