The sea palm is found along the western coast of North America, on rocky shores with constant waves.

It is one of the few algae that can survive and remain erect out of the water; in fact, it spends most of its life cycle exposed to the air.

Postelsia was first scientifically described by Franz Josef Ruprecht (1814–1870) in 1852 from a specimen found near Bodega Bay in California.

[2] The type specimen collected by Italian paleobotanist Abramo Bartolommeo Massalongo before 1855 is at the Natural History Museum of Verona and was preserved in a lithographic limestone upper and lower slab.

[2] When Italian botanist Achille Forti (1878–1937) worked on the specimens in 1926, they were reinterpreted as close relatives of Postelsia, now known to be a brown algae, which had lived in the coastal waters of the Eocene sea.

[2] Forti renamed the species Postelsiopsis caput-medusae commemorating the fossils' extreme similarity to the extant Postelsia palmaeformis.

[3] 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,[4] and rests on a root-like holdfast.

The diploid sporophyte produces, through meiosis, haploid spores, which drip down through the grooves in the blades onto the substrate, which may be mussels, barnacles, or bare rock.

[5] Postelsia are green in color as juveniles, and change to a golden brown as they age, reaching a height of 50–75 cm (20–30 in).

The cells beneath the epidermis, called the meristoderm, divide rapidly to form rings of growth, again, like a tree.

High wave action may increase nutrient availability and moves the blades of the thallus, allowing more sunlight to reach the organism so that it can photosynthesize.

Some juvenile sporophytes will grow on competing organisms, like mussels or barnacles, and rip them from the rocks when the waves come, gripping them with holdfasts of incredible strength.

Postelsia is a protected species, however, and harvesting it is illegal throughout much of its range, as clipping the blades too low, below the meristem, prevents reproduction.