Fucus spiralis is olive brown in colour with a flattened blade has a distinct midrib. It is similar to both Fucus vesiculosus and Fucus serratus. It is usually spirally twisted without the serrated edges of Fucus serratus, and it does not show the paired air bladders of Fucus vesiculosus. Fucus spiralis normally grows to about 30 to 40 centimeters long and its branching is somewhat irregularly dichotomous. During the summer it may be possible to see bumpy v-shaped swellings with distinct rims at the ends of the fronds - these are its reproductive structures. It attaches to rocks in sheltered to moderately exposed shores in the high intertidal zone with a discoid holdfast and short cylindrical stipe. It lives on the upper shore below the zone of Pelvetia canaliculata and above Fucus vesiculosus and Ascophyllum nodosum. Fucus spiralis spends up to 90 percent of the time out of the water; it can tolerate a high level of desiccation between tides, being able to survive 70 to 80 percent water loss; it dries in order to conserve moisture. Fucus spiralis has a life span of 2 to 5 years, and is mature at 2 years. Reproduction usually begins before or during the second year of growth, from the end of winter through spring and into summer.