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

Family Description:
Members of this family are uncalcified crusts that adhere closely to the substratum and lack rhizoids. Tetrasporangia occur in conceptacles and are zonately, cruciately or irregularly divided. Sexual reproduction has not been confirmed.

Species description:
Rusty Rock is an uncalcified but encrusting red alga that adheres tightly to rocks. It lacks erect branches. Medium to dark red in color, it is so thin (less than 1 mm thick) that it appears partly transparent. It is quite common in tidepools or in protected rock crevices, but will grow on exposed rocks as well.

Botanists have reported only the tetrasporophytic generation in Rusty Rock. Some believe that meiosis has been lost and that the tetraspores produced are diploid (rather than haploid as in other red algae). These diploid tetraspores, which are produced in conceptacles, can germinate and develop directly into another tetrasporophyte, with no intervening gametophytic or carposporophytic generations. Rusty Rock is thus another example of a red alga with an atypical life cycle.
In Washington State, studies have shown that Rusty Rock grows extremely slowly (as little as 1.2 mm per year) and rarely recruits (young individuals are uncommon).

The Plate Limpet (Tectura scutum) is a major grazer of Rusty Rock.