Family Description:
Most members of this family have an alternation of heteromorphic generations in which the gametophyte is the upright phase we recognize, and the tetrasporophyte is a crust. The cruciately divided tetrasporangia occur in chains, often in nemathecia (bands of sori). Gametophytes are cylindrical or flattened, and branched or bladelike. Most gametophytes have a medulla made up of large, colorless cells. Mastocarpus is the exception; it is sometimes placed in its own family, the Petrocelidaceae.
At one time, the genus Gigartina contained both species with isomorphic life phases and species with heteromorphic life phases like Turkish Washcloth. Later, botanists decided that the heteromorphic species were different enough to warrant their own genus, so they took the heteromorphic species out of Gigartina and resurrected the genus Mastocarpus for them. Turkish Washcloth is thus now a species of Mastocarpus, and all but a handful of the other species have been placed in the genus Chondracanthus.

Species description:
The gametophytes are dioecious (male and female individuals are separate), and they grow on rocks or, at least in California, on the valves of the California Mussel (Mytilus californianus). Each forms a rather thick, deep reddish purple (almost black) blade that arises from a crustose base and can branch dichotomously to reach 15 cm (6 in) or more in length. The gametophytic blades are annual, dying back to the crustose base at the end of each season, but the crust itself is perennial, capable of regrowing a new blade annually. When males mature, spermatia are produced over both surfaces of the blades. The spermatia float to female blades and fertilize cells near the tips of papillae located all over both surfaces of the blade. These papillae are very noticeable and give the blade a shaggy or carpeted appearance. The fertilized cells grow into tiny carposporophytes on the female gametophyte, and later these carposporophytes release carpospores.
When the carpospores settle, they germinate and grow into the crustose tetrasporophyte (or, sometimes, directly into another gametophyte). The tetrasporophyte has the common name of Tar Spot, and forms a thick, blackish layer up to 20 cm (8 in) in diameter. It can occur from the extreme lower part of the upper intertidal down into the low intertidal zone. Tar Spot is smooth and has a rather irregular, circular outline. This phase is slow growing (studies in Washington State have shown that it grows only 13 mm or 0.5 in per year) and extremely long lived, perhaps capable of living more than 90 years. Botanists first thought that Tar Spot was an entirely different alga, and named it Petrocelis, but we now know that it is just one phase in the heteromorphic life cycle of Turkish Washcloth. The great longevity of individuals of this species, coupled with its occasional occurrence in parts of Southeast Alaska, might indicate a low recruitment rate. If this is so, then we should be careful not to damage it in any way because it might be eliminated locally. Eventually, Tar Spot produces haploid tetraspores that germinate and grow into gametophytic individuals.

In Baja California, Mexico, gametophytes were found to have photosynthetic rates that were five times those of the crustose tetrasporophytes.

On the outer coast of Washington State, the gametophytes and tetrasporophytes of Turkish Washcloth occur simultaneously at similar tidal heights. When grazers were experimentally excluded, gametophytes increased but tetrasporophytes declined. The reason for tetrasporophytic decline was probably due to their being overgrown and shaded by a thick film of diatoms and small green, brown and red algae. Hence, with respect to local grazer abundance, this species does not put "all its eggs into one basket;" if grazers are absent, both stages can flourish, but if grazers are present, the grazer-resistant tetrasporophytic stage can still carry on the life cycle.

Workers in California have found that the life history of Turkish Washcloth partly depends on latitude. Up to 95% of the female gametophytes from central-southern California ultimately produced the crustose tetrasporophyte. In central-northern California, however, up to 90% of the female gametophytes in two out of three populations gave rise to the next generation of gametophytes without going through a tetrasporophytic stage, while in the third population, up to 60% of the female gametophytes gave rise to a tetrasporophytic phase.

Recent studies on this species have shown that when gametophytes are wet, they evaporate water from their surfaces, which keeps them below ambient air temperatures. Dried individuals cannot evaporate water and can exceed the temperature of the surrounding air, especially when there is little or no wind. Thicker individuals dried out less easily, and individuals that were more branched dried out more readily. In Turkish Washcloth, therefore, the temperature and rate of drying of individuals are controlled by anatomical characteristics. This is likely true for other algae as well.

Researchers working in central California examined the thermal tolerances of female gametophytes of this species. They found that after a two-hour exposure of up to 25°C (77°F) air, the gametophytes showed recovery of photosynthetic rates within 10 minutes of being reimmersed in seawater. At 30°C (86°F) recovery was complete but delayed two hours, and at 35°C (95°F), which was apparently above the upper limit of thermal tolerance, there was no recovery. The rate of photosynthesis in air also decreased with increasing desiccation, and below 25% water content in the thallus, there was no net photosynthesis. These experiments indicate that when Turkish Washcloth is subjected to heating and desiccation during low tide, photosynthesis is inhibited.

The tetrasporophytes of Turkish Washcloth collected from southern British Columbia/northern Washington State were able to withstand submersion for a week in water at a temperature of 28°C (82°F), making this among the most thermally tolerant of all of our species of algae. The gametophytes were able to withstand a still impressive 25°C (77°F).

In a study performed in central California, Turkish Washcloth blades showed decreased drag as water flow increased, apparently because the increased water flow changed the shape of the blades. Papillae on the blades increased blade drag (drag decreased when papillae were removed). When individuals were pulled, only 12% failed because the holdfast came off the rock. In 88% of cases, failure was due to stipe breakage, which allowed the holdfast to persist and perhaps grow more blades later. Workers found that the thickness of the stipe did not vary with blade size, indicating that blade size is apparently limited by stipe failure.

Limpets are among the intertidal grazers that eat this species, and one report suggests that the Tar Spot phase is a preferred food of Plate Limpets (Tectura scutum). The gametophyte has moderate caloric value (3.38 Calories per gram of dry weight), but the caloric value of the tetrasporophyte is unknown.

Turkish Washcloth is present throughout our area. We have seen it at Sunshine Cove, near Juneau, Alaska, where it was especially abundant in April of 1998 after a mild winter.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Petrocelis franciscana
Gigartina cristata
Gigartina dichotoma
Gigartina mamillosa (sensu Doty, Scagel)
Gigartina papillata
Gigartina sitchensis
Petrocelis franciscana
Petrocelis middendorffii