Description: Plants of the largest species reach 140 cm in length. Thalli are erect, usually in clusters, from a crustose base and form linear-lanceolate to broadly foliose blades. Cystocarps are dispersed and embedded in the thallus, the carposporophytes being surrounded by a filamentous hull. Spermatangia form in extensive sori on the blades. Tetrasporangia arise in short chains laterally derived from cells within medullary filaments.
Information contributed by: G.T. Kraft. The most recent alteration to this page was made on 16 Mar 2016 by M.D. Guiry.
Comments: The typification and nomenclatural history of this important carrageenanophyte are extremely complex (Parkinson, 1981), and the final composition of the genus probably awaits major changes. Leister (1977) has foreshadowed that some or many of the species now placed in Iridaea will be transferred to the undescribed genus Boryella based on differences in the ontogeny of the involucres of sterile filaments that surround the carposporophyte during its initiation and development, as well as the mode of tetrasporangial formation. Carrageenans in species of Iridaea vary with the ploidy level (McCandless et al. 1975; Waaland 1975), permitting identification of juvenile and sterile individuals as gametophytes or sporophytes. Utilizing this character, Dyck et al. (1985) assessed and speculated on the possible causes of eastern Pacific populations that were highly skewed to one generation or the other, and May (1986) considers possible causes of a northeastern Pacific population of one species that was 83% gametophytes and 17% sporophytes. Hannach and Waaland (1986) summarize knowledge of the biology, ecology, and economic potential of Iridaea, concluding that our understanding is not yet at the point of managing existing wild populations to provide sustained yields or to achieve successful commercial cultivation. Distribution: The centre of distribution for the species now credited to Iridaea is western South America, with a major extension up the North American coast through southern Alaska to northern Japan. Other species occur on the islands of the Subantarctic (Ricker 1986).