UC specimens and range limits for Postelsia palmaeformis

• Blue markers: specimen records
• Yellow marker: type locality, if present
• Red markers: endpoints of range from literature

View map from the Consortium of Pacific Northwest Herbaria

Notes: Before the 1983-84 El Niño, the southern limit of Postelsia was at the headland north of Diablo Cove, San Luis Obispo Co., California (35.213018,-120.861111). The population was lost and never recovered, probably because the Diablo Canyon Nuclear Power Plant began discharging warm water in 1985. Currently, the southernmost population is on the first headland south of Point Buchon (35.251192,-120.897245) (S. Kimura, pers. comm.). The published northern limit is Hope Island, British Columbia, Canada.

Status: This species is easy to identify.

Habitat: Restricted to wave-exposed, intertidal zone rocky shores, often, but not always, associated with Mytilus californianus Conrad, 1837, the California mussel (Dayton 1973; Paine 1979, 1988). Physiological stresses associated with emersion limit the upper distribution of Postelsia through declines in growth, survivorship, and reproductive output; both physiological and ecological performance, expressed as reductions in growth and reproductive output, but not survivorship, decline at the lower edges of its vertical range (Nielsen et al. 2006).

Life History: Alternation of heteromorphic phases, with a macroscopic, annual sporophyte and dioecious microscopic gametophytes (Myers 1925). Dispersal distances are short, resulting in closely related individuals in local populations (Coyer et al. 1997). In fact, Postelsia gametophytes frequently self-fertilize, with little cost in fitness (Barner et al. 2011).

Conservation: Postelsia is a protected species in California, and its harvest is regulated by the California Department of Fish and Wildlife. Closed to non-commercial harvest. A precautionary approach to management of the commercial Postelsia harvest should: (1) mandate frond trimming rather than taking the entire individual, (2) limit collection to once a year and (3) close the commercial season before the onset of reproduction (Thompson et al. 2010).

Associated Taxa: California mussel (Mytilus californianus), goose neck barnacles (Pollicipes polymerus), Endocladia muricata, corallines (e.g., Corallina vancouveriensis, Bossiella plumosa, B. frondifera), Pylaiella gardneri, Ectocarpus commensalis, Pyropia gardneri

Search Sequences in GenBank

Illustration from DeCew's Guide to the Seaweeds of British Columbia, Washington, Oregon, and Northern California

Postelsia Ruprecht 1852

Sporangial thalli with relatively small holdfast of stout, branched haptera. Stipe erect, cylindrical and hollow, tapering slightly from base to apex. Apex of stipe with many short, radially disposed, simple branches, each terminating in single blade. Branch and blade splitting longitudinally into 2 blades and branches, usually of equal size, the splitting beginning at junction of branch and blade. Blades sharply pointed, narrowly linear, the margins dentate. Both flattened surfaces of blade with deep, parallel, longitudinal grooves, the grooves of 1 surface alternating with those of other. Sporangia in linear sori, these lining grooves of blades.

Postelsia palmaeformis Rupr.

Ruprecht 1852: 75; Setchell & Gardner 1925: 625; Smith 1944: 142.

Sporangial thalli to 60 cm tall, usually growing in extensive stands; stipes erect and blades pendant when plants are exposed by recession of tide; mature plants golden brown, with 100 or more blades, these to 25 cm long; sporangia first produced in late spring; blades becoming eroded after fruiting; spores released during low tide and remaining in grooves of blades, dripping off the slender tips onto holdfast or nearby rock. Locally abundant in areas exposed to surf, saxicolous, high to midtidal, Vancouver I., Br. Columbia, to Morro Bay (San Luis Obispo Co.), Calif. Type locality: Bodega Bay (Sonoma Co.), Calif.

Excerpt from Abbott, I. A., & Hollenberg, G. J. (1976). Marine algae of California. Stanford University Press, Stanford, California. xii [xiii] + 827 pp., 701 figs.

Notes: The southern limit on the first headland south of Point Buchon (35.251192,-120.897245).