When you look at this image, there probably will be little doubt in your mind why we call that growth “Rockweed.”
It’s other common name, “Knotted Wrack,” also has a partly obvious origin: this organism is “knotted” with little air bladders that float its “blades” up at higher tide to get needed sunlight. I found it interesting to learn that it’s called a “wrack” because “sea wrack” is the old name for “seaweed.” (Even more interesting: historically, “wrack,” once meant something cast up from the sea onto the shore. That word evolved into “wreck” and “ship wrack” became “ship wreck.”)
The scientific name for this seaweed is Ascophyllum nodosum and, not surprisingly, “nodosum” means “full of knots.” There are other, similar seaweed species that are also commonly known as Rockweed simply because of their trait of anchoring themselves on rocks.
Rockweed is not a weed or true plant and it is not limited to rock habitats. It’s one of our brown marine algae. It has no roots; it uses a “holdfast” mechanism to glue itself to hard surfaces, including pier pilings. But, it’s often ripped from its base by rough seas and can be harvested mechanically or by hand for conversion to fertilizer and other usages.
In Maine, there’s tension between many owners of intertidal shorefronts who refuse to permit commercial harvesting of their Rockweed, especially mechanical cutting by Canadian interests. Basically, the owners’ primary concern is that Rockweed should be allowed to flourish because it provides an environment and food source for over 100 marine species. The harvesters and their supporters primarily argue that the organism is renewable and harvesting it provides needed jobs. (Images taken in Brooklin, Maine, on March 8 and 6, 2024.)