Irish Moss

Chondrus crispus is a relatively small sea alga, reaching up to a little more than 20 centimetres (7+3⁄4 in) in length. It grows from a discoid holdfast and branches four or five times in a dichotomous, fan-like manner. The morphology is highly variable, especially the broadness of the thalli. The branches are 2–15 mm broad and firm in texture, and the color ranges from bright green towards the surface of the water, to deep red at greater depths. The gametophytes (see below) often show a blue iridescence at the tip of the fronds which is attributed to structural coloration and fertile sporophytes show a spotty pattern. Mastocarpus stellatus (Stackhouse) Guiry is a similar species which can be readily distinguished by its strongly channelled and often somewhat twisted thalli. Irish moss undergoes an alternation of generation lifecycle common in many species of algae. The two distinct stages are the sexual haploid gametophyte stage and the asexual diploid sporophyte stage. In addition, a third stage – the carposporophyte – is formed on the female gametophyte after fertilization. The male and female gametophytes produce gametes which fuse to form a diploid carposporophyte, which forms carpospores, which develops into the sporophyte. The sporophyte then undergoes meiosis to produce haploid tetraspores (which can be male or female) that develop into gametophytes. …

Chondrus crispus is commonly found along the shores of Ireland and the coast of Europe including Iceland, the Faroe Islands, western Baltic Sea to southern Spain. It is found on the Atlantic coasts of Canada and recorded from California in the United States to Japan. However, any distribution outside the Northern Atlantic needs to be verified. There are also other species of the same genus in the Pacific Ocean, for example, C. ocellatus Holmes, C. nipponicus Yendo, C. yendoi Yamada et Mikami, C. pinnulatus (Harvey) Okamura and C. armatus (Harvey) Yamada et Mikami.

Chondrus crispus is found growing on rock from the middle intertidal zone into the subtidal zone, all the way to the ocean floor. It is able to survive with minimal sunlight. C. crispus is susceptible to infection from the oomycete Pythium porphyrae.

C. crispus is traditionally used fresh as a thickening agent in carrageen pudding, a milk-based dish eaten in Scotland and Ireland. Likewise, it is an industrial source of carrageenan commonly used as a thickener and stabilizer in milk products, such as ice cream and processed foods. During World War 2 the allies used carageenan as an alternative to agar which had been cut off due to Japan being the sole producer. In Europe, it is indicated as E407 or E407a. It may also be used as a thickener in calico printing and paper marbling, and for fining beer. Irish moss is frequently used with Mastocarpus stellatus (Gigartina mamillosa), Chondracanthus acicularis (G. acicularis), and other seaweeds, which are all commonly found growing together. Carrageenan may be extracted from tropical seaweeds of the genera Kappaphycus and Eucheuma.