Scytosiphon lomentaria

Thallus (gametophyte) simple, unbranched, cylindrical, with constrictions at more or less regular intervals, solid when young, hollow at maturity, sometimes compressed, twisted, shortly stipitate, golden- or olive-brown, 0.2–0.7 (–2.0) m high, 4–10 mm diam., tapering toward small discoidal holdfast bearing tufts of several thalli. In transverse section, medulla composed of large thick-walled cells decreasing to one layer of small cuboidal superficial cells. Uniserial plurangia (65×4–5 μm), clavate paraphyses and hairs develop from superficial cells. Sporophytic plant microscopic, crustlike. Growing in upper subtidal on rocky, and epiphytic on seaweeds.

Subarctical, temperate and subtropical waters.