Palmaria palmata
Scientific classification
Clade:	Archaeplastida
Division:	Rhodophyta
Class:	Florideophyceae
Order:	Palmariales
Family:	Palmariaceae
Genus:	Palmaria
Species:	P. palmata
Binomial name
Palmaria palmata (L.) F.Weber & D.Mohr
Synonyms [1]
Ceramium palmatum (Linnaeus) Stackhouse, 1797 Delesseria palmata (Linnaeus) J.V.Lamouroux, 1813 Delesseria sobolifera (M.Vahl) J.V.Lamouroux, 1813 Fucus bullatus O.F.Müller, 1777 Fucus caprinus (Gunnerus) Vahl, 1794 Fucus delicatulus (Gunnerus) Vahl, 1797 Fucus dulcis S.G.Gmelin, 1768 Fucus foliaceus Ström, 1788 Fucus ovinus Gunnerus, 1766 Fucus palmatus Linnaeus, 1753 Fucus rubens Esper, 1799 Fucus rubescens Sommerfelt, 1826 Fucus sarniensis Roth, 1806 Fucus soboliferus M.Vahl, 1792 Halymenia palmata (Linnaeus) C.Agardh, 1817 Halymenia sobolifera (M.Vahl) C.Agardh, 1817 Palmaria expansa Stackhouse, 1809 Palmaria lanceolata Stackhouse, 1809 Rhodymenia palmata (Linnaeus) Greville, 1830 Rhodymenia sobolifera (M.Vahl) Greville, 1830 Sphaerococcus palmatus (Linnaeus) Wahlenberg, 1826 Sphaerococcus sarniensis (Roth) C.Agardh, 1817 Sphaerococcus soboliferus (M.Vahl) Kützing, 1843 Ulva caprina Gunnerus, 1772 Ulva delicatula Gunnerus, 1772 Ulva palmata (Linnaeus) Withering, 1796 Ulva sobolifera (M.Vahl) Lyngbye, 1819

Palmaria palmata, also called dulse, dillisk or dilsk (from Irish/Scottish Gaelic duileasc/duileasg), 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 söl [ˈsœːl̥], it has been an important source of dietary fiber throughout the centuries.

The earliest record of this species is on the island of Iona, Scotland where Christian monks harvested it over 1,400 years ago.^[2]

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 50 centimetres (20 in) long and 3–8 cm (1.2–3.1 in) in width which can bear flat, wedge-shaped proliferations from the edge.^[3][4] The blade consists of an outer cortex of small cells enclosing a medulla of larger cells up to 0.35 thick.^[5][6]

The reference to Rhodymenia palmata var. mollis in Abbott and Hollenberg (1976),^[7] is now considered to refer to a different species: Palmaria mollis (Setchel et Gardner) van der Meer et Bird.^[8][9]

Dulse is similar to another seaweed, Dilsea carnosa,^[10] but Dilsea is more leathery with blades up to 30 cm (12 in) long and 20 cm (7.9 in) 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.^[11]

The full haplodiploid life history was not fully explained until 1980.^[12] There are two phases in the life-history, with a haploid phase that is dioecious, with separate male and female plants. The large haploid plants are male, having sporangia. Spermatial sori occur scattered over most of the frond of the haploid male plant. The male plants are blade-like and produce spermatia which fertilize the carpogonia of the female crust. The female gametophyte is very small stunted or encrusted, the carpogonia, the female nucleus, apparently occurring as single cells in the young plants. The female plants are minute, less than 1 mm), and after fertilization become overgrown by the resulting diploid plant.^[13] Tetraspores occur in scattered patches sori (spores) on the mature diploid blade. The adult tetrasporophyte produces tetraspores meiotically in fours.^[3][14]

P. palmata is to be found growing from mid-tide of the intertidal zone (the area between the high tide and low tide) to depths of 20 m or more in sheltered and exposed shores.^[14]

Dulse is commonly used as food and medicine in Ireland,^[15] Iceland and Atlantic Canada. It can be found in many health food stores or fish markets and can be ordered directly from local distributors. It is also used as fodder for animals in some countries.

Dulse is a good source of minerals and vitamins compared with other vegetables, contains all trace elements needed by humans, and has a high protein content.^[2] Dulse contains iodine, which prevents goitre.

It is commonly found from June to September and can be picked by hand when the tide is out. When picked, small snails, shell pieces, and other small particles can be washed or shaken off the plant, which is then spread to dry. Some gatherers may turn it once and roll it into large bales to be packaged later.

Fresh dulse can be eaten directly off the rocks before sun-drying. Sun-dried dulse is eaten as is or is ground to flakes or a powder. When used in cooking, dulse's properties are similar to those of a flavour-enhancer. In Iceland, the tradition is to eat it with butter.^{[citation needed]}. It can be pan-fried quickly into chips, baked in the oven covered with cheese, with salsa, or simply microwaved briefly. It can be used in soups, chowders, sandwiches, and salads, or added to bread or pizza dough. Finely diced, it can be used as a flavour enhancer in meat dishes, such as chili, in place of monosodium glutamate.

In Ireland dulse can be used to make "White Soda Bread".^[16] In Ballycastle, Northern Ireland, it is traditionally sold at the Ould Lammas Fair. It is particularly popular along the Causeway Coast. Although a fast-dying tradition,^{[citation needed]} many gather their own dulse. Along the Ulster coastline from County Down to County Donegal, it is eaten dried and uncooked as a snack. It is commonly referred to as dillisk on the west coast of Ireland. Dillisk is usually dried and sold as a snack food from stalls in seaside towns by periwinkle sellers.

Researchers at Oregon State University's Hatfield Marine Science Center have selected a fast-growing strain of Pacific dulse (P. mollis). Originally intended as a feed for abalone farming, they claim their strain of the seaweed tastes like bacon when fried.^[17][18]

P. palmata is the only species of Palmaria found on the coast of Atlantic Europe. It can be found from Portugal to the Baltic coasts and on the coasts of Iceland and the Faroe Islands.^[19] It also grows on the shores of Arctic Russia, Arctic Canada, Atlantic Canada, Alaska, Japan, and Korea.^[14] Records of P. palmaria from California are actually of Palmaria mollis.^[9]

Galls, possibly produced by parasitic nematodes, copepods, or bacteria, are known to infect these plants. They were recorded as "outgrowths of tissue produced by the presence...of an animal."^[14][20]

• Grubb, V.M. 1923. Preliminary note on the reproduction of Rhodymenia palmata, Ag. Annals of Botany 37: 151–52.
• Pueschel, C.M. 1979. Ultrastructure of the tetrasporogenesis in Palmaria palmata (Rhodophyta). Journal of Phycology 15: 409–424.
• South, G.R. and Hooper, R.G. 1980. A Catalogue and Atlas of the Benthic Marine Algae of the Island of Newfoundland. pp. 1–136. Memorial University of Newfoundland Occasional Papers in Biology.
• Lennon, B.W. and Doyle, E. Wild Food. The O'Brien Press, Dublin. ISBN 978-1-84717-467-3

• AlgaeBase
• Palmaria palmata Archived 2014-11-07 at archive.today at Michael Guiry's Seaweed Site
• "Dulse" . Encyclopædia Britannica. Vol. 8 (11th ed.). 1911. p. 653.
• "Dulse" . New International Encyclopedia. 1905.