Narrow compressed stipe expands into strap-like blade, usually inrolled to form a channel, with thickened margins. Repeatedly dichotomously branched, axils acute. Upper part of frond with papillae to 10 mm or more long on surfaces and margins on female plants.
Male plants lack papillae but are generally rare.
On rocks in lower intertidal, often in large continuous mats, widespread and abundant. Collected more or less interchangeably with Chondrus crispus for use as Carrageen or Irish Moss. A Carrageen Cheese Cake is shown on this page.