Palmaria palmata, also called dulse, dillisk or dilsk (from Irish/Scottish Gaelic /), red dulse, sea lettuce flakes, or creathnach, is a red alga (Rhodophyta) previously referred to as Rhodymenia palmata. It grows on the northern coasts of the Atlantic and Pacific Oceans. It is a well-known snack food. In Iceland, where it is known as , it has been an important source of dietary fiber throughout the centuries. History The earliest record of this species is on the island of Iona, Scotland where Christian monks harvested it over 1,400 years ago. Description The erect frond of dulse grows attached by its discoid holdfast and a short inconspicuous stipe epiphytically on to the stipe of Laminaria or to rocks. The fronds are variable in shape and colour from deep rose to reddish purple and are rather leathery in texture. The flat foliose blade gradually expands and divides into broad segments ranging in size to long and in width which can bear flat, wedge-shaped proliferations from the edge. The blade consists of an outer cortex of small cells enclosing a medulla of larger cells up to 0.35 thick. The reference to Rhodymenia palmata var. mollis in Abbott and Hollenberg (1976), is now considered to refer to a different species: Palmaria mollis (Setchel et Gardner) van der Meer et Bird. Dulse is similar to another seaweed, Dilsea carnosa, but Dilsea is more leathery with blades up to long and wide. Unlike P. palmata, it is not branched and does not have proliferations or branches from the edge of the frond, although the older blades may split. Life history The full life history was not fully explained until 1980. There are two phases in the life-history, that is it is dioecious, male and female plants grow separately. The large plants are male or have sporangia. The female plants are minute, less than 1 mm) and become overgrown after fertilization by the diploid plant. Tetraspores occur in scattered patches sori (spores) on the mature blade, diploid blade. Spermatial sori occur scattered over most of the frond of the haploid (single cell) male plant. The female gametophyte is very small stunted or encrusted, the carpogonia, the female nucleus, apparently occurring as single cells in the young plants. The male plants are blade-like and produce spermatia which fertilize the carpogonia of the female crust. The adult tetrasporophyte produces tetraspores meiotically in fours. Ecology P. palmata is to