Like all seaweeds, the sporophyte stage of Postelsia consists of a thallus, which is made up of a stem-like stipe topped with possibly over 100 leaf-like blades, and rests on a root-like holdfast. The holdfast anchors the organism to the rocks it lives on.
Like all seaweeds, the sporophyte stage of Postelsia comprises a thallus, consisting of a stalk-like stipe topped by numerous leaf-like appendages, and is supported by a root-like base that secures it to the rocks it inhabits.