Postelsia palmaeformis
A kelp that lives mostly out of water on rocky shores.
**Postelsia palmaeformis**, called the sea palm or palm seaweed (not to be confused with the southern sea palm), is a type of kelp belonging to the brown algae group within the SAR supergroup of eukaryotes. It is the sole species in the genus *Postelsia*. This seaweed lives along the western coast of North America, on rocky shores that experience constant wave action. It is one of the few multicellular organisms with differentiated tissues that spends most of its life out of water and is not a member of—or closely related to—animals, fungi, or plants. Although edible, harvesting is discouraged because the species is sensitive to overharvesting.
Indigenous peoples from Central Coast California to British Columbia knew the sea palm. Its uses—for food, medicine, and games—are recorded among the Hesquiaht First Nation, the Ditidaht People, the Nuu-chah-nulth, and the Kashia Pomo. In the Kashaya language of the Kashia Pomo, it is called *qaye*. *Qaye* is prepared three ways: fresh stems chewed raw, cooked in hot ashes, or cut into strips and dried. The species was first scientifically described in 1852 by Franz Josef Ruprecht (1814–1870), based on a specimen collected near Bodega Bay, California, by botanist Ilya Vosnesensky, who worked with Coast Miwok guides. Ruprecht’s paper described one seagrass and five seaweeds, including *Postelsia*. The sea palm appears in textbooks such as *Campbell–Reece Biology* as an example of multicellular protists and of the class Phaeophyceae.
The genus name *Postelsia* honors Alexander Philipov Postels, an Estonian-born geologist and artist who worked with Ruprecht. The species name *palmaeformis* refers to the alga’s superficial resemblance to true palms.
Fossils from Monte Bolca, a lagerstätte near Verona, were originally named *Zoophycos caput-medusae* and thought to be trace fossils, but later recognized as plants and renamed *Algarum* by French zoologist Henri Milne-Edwards in 1866. The type specimen, collected by Italian paleobotanist Abramo Bartolommeo Massalongo before 1855, is housed at the Natural History Museum of Verona, preserved in a lithographic limestone upper and lower slab.
Quick Facts
- Genus
- Postelsia
- Species
- palmaeformis
Facts from the source article.
Lore & Background
The sea palm was known by indigenous peoples across its range from Central Coast California to British Columbia, with documented use among the Hesquiaht First Nation, Ditidaht People, Nuu-chah-nulth, and Kashia Pomo. In the Kashaya language, it is called qaye, prepared by chewing fresh stems raw, cooking in hot ashes, or cutting into strips and drying. The species was first scientifically described by Franz Josef Ruprecht in 1852 from a specimen collected near Bodega Bay by botanist Ilya Vosnesensky, who worked with Coast Miwok guides. The generic name Postelsia honors Alexander Philipov Postels, an Estonian-born geologist and artist who worked with Ruprecht, while the specific name palmaeformis describes its superficial similarity to true palms. Fossils from Monte Bolca, a lagerstätte near Verona, were originally named Zoophycos caput-medusae and previously thought to be trace fossils, but were later found to be plants instead and given the name Algarum by French zoologist Henri Milne-Edwards in 1866. 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. 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. Forti renamed the species Postelsiopsis caput-medusae commemorating the fossils' extreme similarity to the extant Postelsia palmaeformis. The appearance of the fossil is a holdfast on the bottom, with a stem-like stipe between there and the fronds which are about 5 cm to 10 cm. In life, the fronds would have been held vertically in the water. Postelsia has two distinct morphologies: one for its diploid, monoicous sporophyte stage, which is the dominant portion of the life cycle, and one for its smaller, haploid, dioecious gametophyte stage.
Reader's Guide
Postelsia palmaeformis holds significance as a textbook example of multicellular protists and of the class Phaeophyceae, used in works such as the Campbell–Reece Biology textbook. Its life cycle involves alternation of generations typical of brown algae: the diploid sporophyte produces haploid spores via meiosis, which develop into male and female gametophytes; fertilization yields a diploid zygote that grows into a new sporophyte. The species is annual, with juveniles green and aging to golden brown, reaching 50–75 cm in height. The stipe thickens via meristoderm cell division, forming growth rings, but remains flexible to withstand wave action.
Sea palms inhabit the middle to upper intertidal zones of rocky shores from Vancouver Island to central California, thriving in high wave action that increases nutrient availability, sunlight exposure, and removes competitors like California mussels. Studies show Postelsia grows in greater numbers when mussels are present, possibly because mussels protect developing gametophytes or prevent competing algae like Corallina or Halosaccion. Spores are released at low tide and fall within a few meters of the parent, leading to dense aggregations. Juvenile sporophytes may grow on mussels or barnacles, ripping them from rocks with strong holdfasts.
Epiphytes include the brown algae Ectocarpus commensalis and Pylaiella gardneri (an obligate epiphyte), and red algae Microcladia borealis and Porphyra gardneri, which are not harmful. Edibility is noted, but harvesting is discouraged due to sensitivity to overharvesting; it is illegal in British Columbia, Washington, and Oregon, while in California recreational harvesting is illegal but regulated commercial harvesting is legal.
Did You Know?
- The fossil relative Postelsiopsis caput-medusae was originally misidentified as a trace fossil named Zoophycos caput-medusae.
- The Kashia Pomo people call the sea palm qaye and prepare it by chewing fresh stems raw, cooking in hot ashes, or drying cut strips.
- The stipe of Postelsia thickens via meristoderm cell division, forming growth rings similar to a tree trunk.
More in Brown Macroalgae and Kelp, Part 2 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced