Alaria marginata Postels & Ruprecht

Type locality: This species has been assigned a neotype locality of Fort Ross, California USA (Widdowson 1971) since no specimens were collected from the original reported type locality of Unalaska Island, Alaska (Guiry 2013).

Common name: The winged kelp also known as Wakame in Japanese (McConnaughey 1985).  The root “ala” in the genus Alaria is Latin for wing and the species name marginata is Latin for “margined” (Stern 1973) referring to the wing-like reproductive blades, known as sporophylls, that grow from either side of the stipe below the main vegetative blade (Figure 1).

Taxonomy: Ochrophyta: Phaeophyceae: Laminariales: Alariaceae: Alaria

Image of Alaria marginata

Figure 1. Voucher specimen of Alaria marginata collected at Eagle Cove San Juan Island, WA (A. Holdfast to vegetative blade, B. middle portion of vegetative blade, and C. senescent and eroding terminal end of vegetative blade).


Alaria marginata is a marine species of macroalgae typically chocolate to golden brown in color.  This seaweed can be identified by the prominent midrib that runs the length of its main vegetative blade (Figure 1).  The vegetative blade is attached to a stipe that terminates in a hapterous holdfast (Figure 1A.). Basal, lateral sporophylls bear dense aggregations of unilocular sporangia known as sori (singular, sorus) (Figure 2).

Distribution: Alaria marginata is a marine species of macroalga commonly found in the wave exposed, lower intertidal zone of the Pacific coast of Asia and North America (Widdowson 1971).  Specimens have been recorded from Alaska through the Aleutian Islands to just north of Point Conception, California with a few records reported for the Commander Islands and Japan.  The earliest specimen recorded on San Juan Island, Washington in the Friday Harbor Laboratories Herbarium was collected in 1908.

Site Date(s) of collection
Minnesota Reef 1916, 1963
Whidbey Island Nov 1963, 1964
Mt. Dallas Beach, San Juan Islands, WA Jun 1961, Jul 1961, Jul 1962
Friday Harbor Tires May 1989
Friday Harbor Dock April 1989
Deadman Bay 1964
Turn Island June 1961
American Camp July 1961, June 1962
Image of Alaria marginata sporophyll

Figure 2. Close up of an Alaria marginata sporophyll with a sorus.

Vouchers: PHYKOS # 00090 (Figure 1).

Research Notes: Alaria marginata is an annual alga that grows on rocks and appears in late winter/early spring, becoming reproductive by fall (McConnico 2005).  As wave action increases the vegetative blade begins to senesce and erode (Figure 1C.).  By October, in California populations, growth rates are equivalent to erosion rates resulting in no net growth.  This process appears to be escalated on San Juan Island, WA where thalli can be found with senescent and eroded blades as early as June (R. Romero personal observations, Figure 1).  This acceleration of senescence may be related to greater summer wave action, sun exposure during spring tides or differences in community interactions. 

Alaria marginata is competitively inferior to the kelp, Saccharina sessilis in the rocky intertidal zone of Washington (Druehl 1969).  When S. sessilis has been removed and zoospores are allowed to colonize, A. marginata dominates areas where herbivores are excluded (Dethier and Duggins 1988, Paine 2002).  S. saccharina is able to outcompete A. marginata because it isn’t as susceptible to herbivory.  Similarly, persistence of California populations where Kathrina and S. sessilis are not found has been attributed to suppression of competitiors by A. marginata.  Dense aggregations of A. marginata with blades reaching 3m in length (Figure 3) allow this kelp to out compete others for space and light (McConnico 2005). Although, Paine (2002) observed a positive correlation between cover of A. marginata and number of sporelings it has been suggested that abrasion by A. marginata canopies may have a negative effect on sporeling recruitment (McConnico 2005).  Most of the literature on A. marginata relates to identification and taxonomic status, leaving many questions of ecological importance unanswered. 

Figure 3. Dense aggregation of Alaria marginata thalli and canopy at Eagle Cove San Juan Islands, WA.

Figure 3. Dense aggregation of Alaria marginata thalli and canopy at Eagle Cove San Juan Islands, WA.

Literature Cited:

Dethier, M. N., Duggins, D. O. 1988. Variation in strong interactions in the intertidal zone along a geographical gradient: a Washington-Alaska comparison. Mar Ecol-Prog Ser. 50:97-105.

Greville , R.K. 1830. Algae Britannicae, or, Descriptions of the Marine and other Inarticulated Plants of the British Islands, Belonging to the Order Algae. Maclachlan & Stewart, Edinburgh.

M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 30 June 2013.

McConnico, L. A. and M. S. Foster. 2005. Population biology of the intertidal kelp, Alaria marginata Postels and Ruprecht: A non-fugitive annual. J Exp Mar Biol Ecol. 324:61-75.

McConnaughey, E. 1985. Sea Vegetables: harvesting guide and cookbook. pp. 239. Happy Camp, California: Naturegraph Publ. Inc..

Paine, R.T. 2002. Trophic control of production in a rocky intertidal community. Science. 296: 736–739.

Stern W.T. 1973. Botanical Latin: History, grammar, syntax, terminology and vocabulary. Newton Abbot: David & Charles 566p.

Widdowson, T.B. 1971. A taxonomic revision of the genus Alaria Greville. Syesis 4: 11-49.

Vadas, R.L. 1968. The ecology of Agarum and the kelp bed community. PhD Thesis. University of Washington, Seattle, Washington, USA.

Yendo, K. 1919. A monograph of the genus Alaria. J. Coll. Sci., Imp. Univ. Tokyo 43: 1 –145.

Links to additional resources: Kelp Life History animation by the Monterey Bay Aquarium Research Institute

Alaria marginata on Algaebase

Page Authors & Affiliations

Rosemary Romero

Department of Integrative Biology, University of California, Berkeley