Sagassum filipendula C.Agardh is highly distinctive when collected attached in the NW Atlantic flora (Image A). It is among the few larger (to 1 m in length) and coarser brown algal species in our flora and is dark to light (yellowish) brown in colour and attached by an irregular crustose to conical holdfast. The branched terete axes bearing round bladders (3-5mm diam.) on short stalks as well as serrate blades (especially developed lower on the plants) with a central midrib and obvious cryptostomata (sterile cavities similar to conceptacles, producing hairs, but lacking reproductive structures) is unique in our flora (Image A).
We have only a few records, all from south of Cape Cod, typically from low intertidal pools to the shallow (1-4 m) subtidal on rock, cobble or shells. However, other species of Sargassum, notably S. fluitans (Børgesen) Børgesen and S. natans (Linnaeus) Gaillon, can come in as drift material on the Gulf Stream. Consequently Sears (2002) should be consulted if drift plants are encountered.
Image A. Subtidal (3 m) specimen growing on rock from near Woods Hole, MA (GWS017882). Arrow indicates one of the characteristic floats on this species.