The term “seaweed” refers to a group of marine organisms called macroalgae. Many people think of them as plants, but while they do share some similarities (e.g., photosynthesis), seaweeds actually belong to an entirely different kingdom: Protista. The larger group of macroalgae called seaweeds are further classified into red, green and brown alga. One of the easiest brown seaweeds to identify is the sea potato (Leathesia difformis): a yellowish-brown, lumpy sac-like seaweed, often with various dips, divots and furrows when mature. When young, sea potatoes are round and solid, but as they mature they become hollow and take on their more convoluted form. At full size, each individual sea potato is approximately 3 to 5 inches in diameter, and in my opinion, looks nothing like an actual potato. I’ve always thought of them as looking more like little disembodied brains than like potatoes. What do you think they look like? Potatoes? brains? or something else entirely?

Like many seaweeds, sea potatoes attach to another surface using a holdfast (seaweeds do not have true roots) to ensure they they stay in an area with the proper depth and sunlight for adequate photosynthesis. While many attached seaweeds, such as knotted wrack (Ascophyllum nodosum) and rockweeds (Fucus sp.), will attach directly to rocks or other hard substrates, the sea potato is epiphytic. This means it is more likely to grow attached to other seaweeds. On a recent excursion to one of the Boston Harbor Islands, I found sea potatoes quite common among the Irish moss (Chondrus crispus) and rockweed in the lower intertidal zone. But these bulbous seaweeds are often dislodged during storms or other high wave events, and are can be found washed up on the beach (with or without their host) as part of the wrack line.