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Sargassum horneri

(Turner) C. Agardh

Key Characteristics

  • Clusters of symmetrical, fern-like blades from spiny cylindrical stipes
  • Many elliptical floats, some with bladelets at the tip
  • Subtidal plants large (>1m), eroding back to holdfasts in winter
  • Reproductive receptacles large, shaped like chili peppers

Image Gallery (click for more)

Database links

UC specimens and range limits for Sargassum horneri

  • 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: This aggressive invader from Asia was first observed in California in 2003 in Long Beach Harbor; it was found in 2006 at Big Fisherman Cove, Santa Catalina Island (Miller et al. 2007). It has subsequently spread (Marks et al. 2015) to Santa Barbara, Ventura, Orange, Los Angeles, and San Diego Cos. on the mainland and San Clemente, Santa Barbara, Anacapa, and Santa Cruz islands. Also found in the drift at San Miguel and Santa Rosa islands. It has also spread rapidly south to Isla Navidad, Baja California, Mexico. See Illustration.

Status: This recent addition to the flora was probably brought to California from Asia via shipping and spread via recreational boat traffic. cox3 sequences (469 bp in length) from 6 individuals from the 3 sites at Catalina and 3 samples from 3 sites in the Seto Inland Sea, Japan region were identical.

Habitat: Occasional in low intertidal, often abundant in subtidal

Life History: Diplontic, with gametic meiosis; monoecious. Grows quickly in spring and summer, eroding back to stipes and holdfasts in the winter.

Search Sequences in GenBank

Sargassum C. Agardh 1820

Thalli annual or perennial, attached by irregular, solid holdfast or by rhizoidal outgrowths from main axis. Main axis sometimes slightly differentiated into basal portion with flattened, elongate "leaves" and upper portion bearing shorter appendages, these sometimes radially arranged. "Leaves" with midrib and cryptostomata. Pneumatocysts common. Receptacles on special branches and developing in axils of "leaves." Oogonia and antheridia as in family. Both monoecious and dioecious species in Calif. flora.

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: Not in Marine Algae of California.

Classification: Algaebase


Vertical Distribution: Low intertidal - subtidal

Frequency: Rare to abundant

Substrate: Rock

Type locality: Strait of Korea

Specimen Gallery (click for more)

Copyright © 2018 Regents of the University of California
Citation for this page: Sargassum horneri, in Kathy Ann Miller (ed.), 2018 California Seaweeds eFlora, [accessed on October 21, 2018]
Citation for the whole website: Kathy Ann Miller (ed.) 2018. California Seaweeds eFlora, [accessed on October 21, 2018].

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