E-Flora BC: Electronic Atlas of the Flora of British Columbia

Petalonia fascia (Muller) Kuntze 1898
false kelp

Introduction to the Algae
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Distribution of Petalonia fascia
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Ocean Biogeography Information System (global distribution)

Species Information

Family Description:
Macroscopic plants are tubular, saccate, or foliose. This phase represents the gameto-phyte, which bears only plurilocular reproductive structures. In some species, this phase alternates with a crustose phase that resembles Ralfsia and bears the unilocular reproductive structures. Such crusts are assumed to represent the sporophytic phase in the life history of such species. Cells contain only a single chloroplast, which contains a prominent pyrenoid.
Species description:
This annual alga looks like a miniature Laminaria but has only a tiny, discoidal (unbranched) holdfast and lacks the complex internal cell differentiation of the true kelps. False Kelp is a springtime species and can be gone by June in our area. It grows primarily on rocks, and often is found together with Soda Straws (Scytosiphon simplicissimus).

False Kelp is yellowish-brown or greenish-brown with a straplike blade up to 35 cm (about 14 in) tall but is usually smaller. This blade bears shallow ruffles along the margin. The blade is composed of several cell layers; the inner cells are notably larger than the cells of the outer layer. The blade is not hollow like that of the similarly shaped Coilodesme.

False Kelp also forms a crustose phase, resembling the brown alga Ralfsia, that can reach maturity in just 4 weeks. This crustose stage grows when days are long and temperatures relatively high, so the morphology of this species is dependent on environmental cues. Blade formation has also been shown to require a certain minimal concentration of iodine in the water. In New Hampshire, erect fronds were more abundant in winter and spring, but crustose stages did not show a clear seasonality. The tough crustose phase is well adapted to adverse environmental conditions. Laboratory work has shown that some crusts are haploid while others are diploid, so the life cycle of this species is complex and requires further research for complete elucidation.

In Japan, False Kelp is heteromorphic. Erect gametophytes with plurilocular gametangia (or plurangia) produce isogametes that fuse, and the resulting zygotes develop into sporophytes. Unfused gametes can sometimes develop parthenogenetically, to produce crusts that can sometimes develop erect blades. Most sporophytes are encrusting; they bear unilocular sporangia, which produce spores that settle individually and grow into new gametophytes. In Washington State, blades of False Kelp have maximum recruitment (establishment of new individuals) in fall, with drastic population declines in late winter and early spring. The crustose stage, which persists year round, functions as a residual holdfast, forming perhaps several generations of blades.

In our area, False Kelp usually does not form pure stands but grows scattered among other species of algae.

On the east coast of the United States, the blades of False Kelp are a preferred food of the periwinkle snail, Littorina littorea, while the crusts are grazer-resistant. We do not know if periwinkles eat this species in our area. The erect blades of False Kelp are reported to lack both structural and chemical devices to deter herbivores.

Laboratory experiments performed in Washington State have shown that if the blades of False Kelp are deprived of ammonium for a period of time and then resupplied with it, depressed photosynthetic rates can require up to nine days to return to normal. This is important if this species is exposed to patchy nutrients in nature.

Source: North Pacific Seaweeds

Habitat / Range

Bathymetry: mid intertidal to shallow subtidal
World Distribution: Aleutian Islands, Alaska to Baja California, Mexico; Arctic; western North Pacific; North Atlantic; Chile; Mediterranean; North Sea; Baltic

Source: North Pacific Seaweeds

Synonyms and Alternate Names

Fucus fascia
Ilea fascia
Petalonia debilis
Phyllitis fascia

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General References