Ahnfeltia plicata vs. Polyides rotunda

Ahnfeltia plicata and Polyides rotunda in Maine

Ahnfeltia plicata and Polyides rotunda are “red” seaweeds (in phylum Rhodophyta) that appear black to brownish red and fade to white at the tips.

They have a bushy morphology with round axes and measure up to ~30 cm tall in Ahnfeltia and ~20 cm in Polyides (both more typically 5 – 10 cm).

They grow in tidepools in the mid intertidal to 20 m subtidally. They may be found in semi-sheltered, sandy environments and on energetic, rocky coast.