Farlowia mollis (Harvey & J.W. Bailey) Farlow & Setchell.

Type locality: Puget Sound, Washington

Etymology: The species name, “mollis” is Latin for soft, pliant (Stern 1973)

Common name: “Farlow’s seaweed” after American botanist William Gilson Farlow (1844-1919).

Taxonomy: Florideophyceae: Rhodymeniophycidae: Gigartinales: Dumontiaceae: Farlowia

Identification: Farlowia mollis has slippery narrow, ribbon or strap-like gametophytes medium to dark red in color (Lindberg and Lindstrom, 2010).  Thalli reach 20cm tall and 1.5 cm wide but are often much shorter.  Branching is optional, but when branched, laterals are fringe-like.  A faint mid-rib and veins are present but often not evident.  F. mollis has a dome-shaped apical cell that cuts of segment cells via transverse divisions (Abbott, 1962). These segment cells divide to form pairs of opposite laterals and a second pair at right angles to the first.  The result is a flattened pseudoparenchymatous thallus construction (see pseudoparenchyma).

Figure 1. Cross-section of Farlowia mollis showing inner cellular structure at 400x magnification.

Figure 1. Cross-section of Farlowia mollis showing inner cellular structure at 400x magnification.

Confusion in distinguishing between terete or  compressed and ribbon-like makes this seaweed easily mis-identified as Prionitis species or Pikea californica. When using the identification key for Southeast Alaska to Oregon the authors refer to terete or compressed (Gabrielson et al., 2012; page 82, step 96) to mean football shaped in cross section (O’Kelly personal communication, Gabrielson et al., 2012). Use of a hand lens or microscope to locate midrib and veins can sometimes help differentiate F. mollis from Prionitis.  Additionally, F. mollis lacks the chlorine bleach smell characteristic of Prionitis.  The only way to differentiate between F. mollis and Pikea californica is to compare reproductive structures(Abbott, 1962).  Reproductive structures of F. mollis thalli can be found in thickened upper portions of lateral branches, while Pikea californica’s reproductive structures are present on spindle-like laterals.


Figure 1. Farlowia mollis at Ruben Tarte County Park San Juan Island, WA

Figure 2. Farlowia mollis at Ruben Tarte County Park San Juan Island, WA

Farlowia mollis is a marine species of red macroalgae that occurs in the low intertidal zone on rocks but can also be found in mid intertidal zone tide pools (Figure 2).  This seaweed can tolerate a range of wave exposure from exposed to semi-protected outer coast habitats (Lindberg and Lindstrom, 2010).  Records of this species have been found for Russia, Japan, and for North America from Alaska to Baja California (Guiry, M.D. & Guiry, G.M. 2013). On San Juan Island specimens can also be found growing on tires attached to the floating dock at Friday Harbor Laboratories.  The earliest collected specimen in the Friday Harbor Herbarium was collected at Newhall, Orcas Island on June 27, 1904.  Based on these herbarim specimens F. mollis has also been reported at the following locations:

Site Date(s) of collection
Argyle Rocks June 1925
Between American Camp and Eagle Cove June 1966
Cattle Point April 1974
Deadman Bay June 1964
East Sound July 1925
Lime Kiln May 1989
Minnesota Reef July 1961, June 1964
Newhall Orcas Island 1904
North Bay Walden Island July 1961
Whidbey Island No year listed


image of Farlowia molis voucher specimen

Figure 3. Voucher specimen of Farlowia mollis collected from a tire on the floating dock at Friday Harbor Laboratories San Juan Island, WA on June 18, 2013.

Vouchers:  (Figure 3)

Research Notes: The seaweed we are familiar with as Farlowia mollis is the gametophyte form. This seaweed exhibits the Polysiphonia-type life history, alternating between macroscopic upright gametophytes and crustose tetrapsorophytes that resemble what   were formerly known as Haematocelis and/or Cruoriopsis (Decew and West, 1981).  Decew and West (1981) were unable to collect tetraspore in lab cultures but field collected tetraspores produced upright F. mollis gametophytes under long-day culture conditions (lO°C, 12 hrs light:12 hrs dark). Most research on this species is taxonomic in nature or descriptive of its life history.  There has been some interest in chemical properties of algal extracts. In particular, extracts of Farlowia mollis have been tested for antiviral properties but they are not recommended for theraputic use as antiviral treatment (Richards et al., 1978).

Literature Cited:

Abbott, I. A. 1962. Structure and Reproduction of Farlowia (Rhodophyceae). Phycologia, 2: 29-37.

Decew, T. C. and West, J. A. 1981. Investigations on the life histories of 3 Farlowia species Rhodophyta Cryptonemeniales Dumontiaceae from Pacific North America. Phycologia, 20: 342-351.

Gabrielson, P. W., Lindstrom, S. C. and O’kelly, C. J. 2012. Keys to the Seaweeds and Seagrasses of Southeast Alaska, British Columbia, Washington, and Oregon, Department of Botany, University of British Columbia.

Guiry, M.D. & Guiry, G.M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 17 July 2013.

Lindberg, M. R. and Lindstrom, S. C. 2010. Field Guide to Seaweeds of Alaska, Alaska Sea Grant College Program, University of Alaska Fairbanks, Fairbanks, Alaska.

Richards, J. T., Kern, E. R., Glasgow, L. A., Overall, J. C., Deign, E. F. and Hatch, M. T. 1978. ANTI-VIRAL ACTIVITY OF EXTRACTS FROM MARINE-ALGAE. Antimicrob. Agents Chemother., 14: 24-30.

Links to additional resources: Farlowia mollis on Algaebase

Page Authors & Affiliations: Rosemary Romero, Department of Integrative Biology, University of California, Berkeley