Gigartina muelleriana, from Baldock (2009).

Belongs within: Gigartinales.

Gigartina is a genus of red algae in which carposporangial chains form grape-like clusters separated by sterile filaments (Hommersand et al. 1993).

Gel weeds
Published 28 May 2021

The red algae of the genus Gigartina are a widespread bunch, most diverse in temperate regions of the southern hemisphere but also found on most coasts of the north. They grow as erect thalli that may come in a variety of forms: foliose or dichotomously branched, cylindrical, compressed or flattened (Hommersand et al. 1993). Like other members of the Gigartinaceae, the family to which they belong, growth is multiaxial (the primary growth axes composed of multiple filaments). The inner cortical and medullary cells are rather loosely arranged and separated by a copious matrix (Hommersand et al. 1999).

Pestle weed Gigartina pistillata, copyright Ignacio Bárbara.

Members of the Gigartinaceae have an isomorphic life history with the alternating haploid gametophyte and diploid tetrasporophyte generations being similar in overall appearance. Historically, Gigartina has included some species that were subsequently found to have a heteromorphic life cycle with very different-looking generations (Guiry & West 1983). Despite the similarities in appearance of the gametophytes to true Gigartina, these species are now thought to belong to a distinct family, the Phyllophoraceae. The specific details of Gigartina reproduction are, as with all red algae, obscenely complicated, but it is on the basis of these details that Gigartina is distinguished from related genera (Hommersand et al. 1993). Gigartina gametophytes may be either monoecious (with male and female gametes formed on a single thallus) or dioecious (with separate male and female individuals). The reproductive structures of the gametophytes are formed near the apex of the thallus on distinct branchlets, pinnules or papillae. Again as is typical for red algae, ova are not released but retained on the gametophyte, and their fertilisation results in the growth of a diploid carposporophyte on the parent gametophyte. The carposporophyte then releases diploid spores (carpospores) that are released to give rise to the tetrasporophyte generation. In Gigartina, the carposporophytes are each surrounded by an envelope of secondary filaments. Filaments of the carposporophyte penetrate between the cells of the envelope and fuse with them to form a placenta composed of heterokaryotic cells (with a mix of haploid and diploid nuclei). Carposporangia are produced in grape-like clusters. In the tetrasporophytes, tetrasporangia develop embedded within the thallus at the boundary between the cortex and the medulla. Tetraspores are released when the tetrasporangium as a whole is released by the breakdown of the containing patch of cortex; the resulting holes can leave the tetrasporophyte thallus with a reticulate appearance.

Mature carposporophyte of Gigartina pistillata, from Hommersand et al. (1993).

Economically, Gigartina species are of most interest to humans as a source of long polysaccharides called carrageenans. Carrageenans are characteristic of the Gigartinaceae; other notable carrageenan producers include the well-known Irish moss Chondrus crispus. Though not digestible by humans (they largely past through the digestive tract unaltered), carrageenans are used in food production to thicken and set liquids in a similar manner to gelatin. According to Wikipedia, the use of Gigartina for food production is known as far back as 600 BC in China. In pre-industrial methods, carrageenan can be obtained by boiling cleaned seaweed and then straining the resulting brew. In modern times, carrageenans are used to provide texture to a wide range of products, including dairy products such as ice cream or yoghurt, processed meats or vegetarian meat substitutes, or cosmetic products such as toothpaste or shampoo. It has even been used in paper production: old-style marbled paper was made by floating ink on a mixture including carrageenan. Truly a versatile little compound!

Systematics of Gigartina

Characters (from Hommersand et al. 1993): Growth by apical or marginal meristems; thalli cylindrical, compressed or flattened, dichotomously branched or foliose, often bearing adventitious marginal or superficial branchlets, pinnules, or papillae. Gametophytes dioecious or monoecious; procarps formed near apex on adventitious branchlets, pinnules or papillae; cystocarps large, subterminal; auxiliary cell forming protrusions bearing gonimoblast initials from inner side, surrounded by a compact envelope; gonimoblast filaments penetrating between cells of envelope, linking to them progressively by cell fusions or secondary pit connections; carposporangial chains derived from uninucleate gonimoblast cells and multinucleate, heterokaryotic envelope cells, and linked to sterile cells and other carposporangia forming an extensive network; mature carposporangia in clusters, separated by cells of the sterile network and surrounded by a common outer envelope; terminal tubular gonimoblast cells fusing with envelope cells; carposporangia, gonimoblast cells, and envelope cells interconnected with broadened pit connections between cells; external pericarp and ostiole present, formed by resumed growth of the outer cortical filaments; carpospores released through ostiole. Tetrasporangial sori raised, elliptical to linear, formed progressively at boundary between inner cortex and medulla; tetrasporangia transformed from inner primary cortical cells and lateral secondary filaments, forming short chains linked to neighboring cells by secondary pit connections; tetraspores released by excision and gelatinous extrusion of sorus.

<==Gigartina Stackhouse 1809 [incl. Chondrodictyon Kützing 1843]HG93
    |--*G. pistillata (Gmelin) Stackhouse 1809HG93 [=Fucus pistillatus Gmelin 1768HG93, G. (Eugigartina) pistillataG64]
    |--G. acicularis [=G. (Eugigartina) acicularis]G64
    |--G. alveata (Turner) Agardh 1851HG93
    |--G. ancistroclada Montagne 1845L27
    |--G. angulata Agardh 1876L27
    |--G. apoda Agardh 1899L27
    |--G. aricularisBBB-S95
    |--G. atropurpurea Agardh 1885L27
    |--G. batracopus Bory de Saint-Vincent 1828BS-V28
    |--G. binghamiae Agardh 1899S57
    |--G. burmanni (Agardh) Agardh 1851L27
    |--G. chapmanni Hooker & Harvey in Harvey 1855HG93
    |--G. chondroides Bory de Saint-Vincent 1828BS-V28
    |--G. clathrata (Decaisne) Rabenhorst 1878 [incl. *Chondrodictyon capense Kützing 1843]HG93
    |--G. clavifera Agardh 1876L27
    |--G. confervoides [=Fucus confervoides]BS-V28
    |--G. contorta Bory de Saint-Vincent 1828BS-V28
    |--G. corymbifera (Kützing) Agardh 1876S57
    |--G. crassicaulis (Agardh) Setchell & Gardner 1933HG93
    |--G. cristata (Setchell) Setchell & Gardner 1933 [=G. mamillosa f. cristata]S57
    |--G. decipiens Hooker & Harvey 1855L27
    |--G. disticha Sonder 1845L27
    |--G. divaricata Hooker & Harvey 1845L27
    |--G. exasperata Harvey & Bailey 1851 [=G. radula f. exasperata]S57
    |--G. fissa (Suhr.) Agardh 1876L27
    |--G. grandifida Agardh 1876L27
    |--G. hypniformis Bory de Saint-Vincent 1828BS-V28
    |--G. insidiosa Agardh 1899L27
    |--G. kroneana Rabenh. 1878L27
    |--G. laciniata Agardh 1876L27
    |--G. latissima (Harvey) Eaton in Agardh 1899 [=G. mamillosa f. latissima]S57
    |--G. lemanaeformis Bory de Saint-Vincent 1828BS-V28
    |--G. livida (Turner) Agardh 1851 [incl. G. pinnata]L27
    |--G. longifolia Agardh 1899L27
    |--G. macrocarpa Agardh 1876L27
    |--G. mamillosa (Goodenough & Woodward) Agardh 1851S57
    |--G. melanotrix Bory de Saint-Vincent 1828BS-V28
    |--G. muelleriana Setchell & Gardner 1933 [=G. flabellata Agardh 1875]HG93
    |--G. orbitosa Agardh 1899L27
    |--G. pachymenioides Lindauer 1949HG93
    |--G. papillata (Agardh) Agardh in Agardh 1846S57
    |--G. polyglotta Agardh 1855L27
    |--G. protea Agardh 1855L27
    |--G. radula (Esp.) Agardh 1847L27
    |--G. rubens Agardh 1899 [incl. G. grandifida var. latifolia Agardh 1876]L27
    |--G. rugulosa [=Rhodomela rugulosa]BS-V28
    |--G. sitchensis Ruprecht in Kjellman 1889S57
    |--G. skottsbergii Setchell & Gardner 1936HG93
    |--G. stellata (Stackhouse) Batters 1902S57
    |--G. teedei [=G. (Eugigartina) teedei]G64
    |--G. unalaschcensis (Ruprecht) Ruprecht in Kjellman 1889S57
    `--G. wehliae Sonder 1871HG93

*Type species of generic name indicated


[BS-V28] Bory de Saint-Vincent, J. B. 1828. Voyage Autour du Monde, Exécuté par Ordre du Roi, Sur la Corvette de Sa Majesté, La Coquille, pendant les années 1822, 1823, 1824 et 1825. Botanique. Cryptogamie. Arthus Bertrand: Paris.

[BBB-S95] Boubezari, K., G. Bitar & D. Bellan-Santini. 1995. Structure et organisation de trois moulières (Mytilus galloprovincialis et Perna perna) de la région d’Alger. Mésogée 54: 63–72.

[G64] Gray, J. E. 1864. Handbook of British Water-weeds or Algae. R. Hardwicke: London.

Guiry, M. D., & J. A. West. 1983. Life history and hybridization studies on Gigartina stellata and Petrocelis cruenta (Rhodophyta) in the North Atlantic. Journal of Phycology 19: 474–494.

Hommersand, M. H., S. Fredericq, D. W. Freshwater & J. Hughey. 1999. Recent developments in the systematics of the Gigartinaceae (Gigartinales, Rhodophyta) based on rbcL sequence analysis and morphological evidence. Phycological Research 47: 139–151.

[HG93] Hommersand, M. H., M. D. Guiry, S. Fredericq & G. L. Leister. 1993. New perspectives in the taxonomy of the Gigartinaceae (Gigartinales, Rhodophyta). Hydrobiologia 260–261: 105–120.

[L27] Laing, R. M. 1927. A reference list of New Zealand marine algae. Transactions and Proceedings of the New Zealand Institute 57: 126–185.

[S57] Scagel, R. F. 1957. An annotated list of the marine algae of British Columbia and northern Washington (including keys to genera). National Museum of Canada Bulletin 150: 1–289.

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