Papillate Seaweed/Sea Tar (Mastocarpus papillatus)

Description: Papillate seaweed is also called Turkish washcloth but that common name is also used by Mastocarpus jardinii so for clarity, we’ll stick with papillate seaweed for Mastocarpus papillatus. This kind of algae has two forms: a crust form and a blade form, which means one encrusts on rocks and the other has actual blades. The crust is the sporophyte stage of life for this algae and looks like a tar spot, giving this algae its other common name, sea tar. The spots can reach 13 cm across and is very slow growing at a rate of only 1.3 cm per year. The gametophyte stage is where we see blades growing off the rock. The blades are flat and oval shaped and have irregular branching, reaching a total of 15 cm long. In mature blades, they develop small projections, giving them a bumpy texture, hence their common name (whether it be papillate or washcloth). The color of these blades can range from a yellow-brown to red-brown or even black.

Habitat: Papillate seaweed is found in abundance in the high to mid intertidal zones, especially in the Pacific Northwest of the United States. In the eastern Pacific Ocean, it ranges from Alaska’s Aleutian Islands to Baja California, Mexico. In the western Pacific Ocean, it is found along Russian and Japanese coastlines. 

Tide Pool Tidbits:

• Previously in history, scientists used to think that the crust form of papillate seaweed was a separate genus from the blade form. The crust form had the common name tar spot seaweed until DNA analysis revealed that the two forms had the same genetic material. It now goes by both names referring to the same algae.

• Larger individuals can reach 90 years old!

• Males have less, or are even lacking, the bumps that are covering the blade surface of females and may also be paler in color.

References: The New Beachcomber’s Guide to the Pacific Northwest by J Duane Sept, Puget Sound Museum of Natural History