Laminaria J.V.Lamouroux, 1813, nom. cons.

Lectotype species: Laminaria digitata (Hudson) J.V.Lamouroux

Original publication: Lamouroux, J.V.F. (1813). Essai sur les genres de la famille des Thalassiophytes non articulées. Annales du Muséum d'Histoire Naturelle 20: 21-47, 115-139, 267-293, plates 7-13.

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Type designated in: Bachelot de la Pylaie, A.J.M. (1830 '1829'). Flore de Terre-Neuve et des Iles Saint-Pierre et Miclon. Livraison [Algae]. pp. 1-128. Paris: Typographie de A. Firmin Didot, rue Jacob, No. 24.

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Description: Life cycle typical for the order Laminariales: diplohaplontic with alternation of large sporophyte bearing unilocular meiosporangia with paraphyses (sori) and microscopic dioecious and oogamous, heteromorphous gametophytes. Chromosome numbers of genus n = 22-31. The sporophytes large (> 1 m) and differentiated into an usually branched, seldom disc-like (L. solidungula, L. yezoensis) or rhizomatous holdfast (L. sinclairii, L. rodriguezii), a stipe and a blade. Stipe cylindrical or compressed, solid or sometimes hollow, always terminating into a single blade. Annual growth rings present in some species. Attachment of haptera by meristoderm-generated rhizoidal cells (Tovey & Moss 1978). Most species with perennial sporophytes (2-18 years old) with a blade that is regenerated from the meristematic region between blade and stipe. Blades entire without median fascia (section: Simplices) or with conspicious median fascia (section: Fasciatae), or blades incompletely or palmately divided into a number of segments (section: Digitatae). Blades without cryptostomata, usually smooth but sometimes ruffled or bullate, no longitudinal ribs or midrib. Unilocular sporangia as sori on both surfaces of blades. Each sporangium joined by an unicellular paraphysis; contains 32 haploid zoospores. Motile zoospores with single chloroplast, without eyespot and flagellar swelling. After settling, zoospores develop into dioecious heteromorphous microscopic gametophytes with oogamous reproduction. Females with large x-chromosome (Evans 1965). Gametogenesis induced by blue light, inhibited by too low or high temperatures, insufficient nutrient supply or lack of iron (e.g.: Lüning & Dring 1972, Motomura & Sakai 1981, tom Dieck 1992, Hsiao & Druehl 1971). Male and female gametophytes one to few-celled or filamentous. Males bear clusters of colorless one-celled antheridia at tips of branches each producing a single biflagellate spermatozoid. Each female gametophyte cell able to develop into a one-celled oogonium producing a single egg with remnants of flagellum (Motomura & Sakai 1988) which is extruded from oogonium, but remains attached to it. Release apparently controlled by a circadian rhythm, mostly during the first 30 minutes of darkness (Lüning 1981). At release of eggs sexual pheromone lamoxirene is secreted causing ejection of spermatozoids from antheridia and attraction to the eggs where fertilization takes place (Lüning and Müller 1978, Müller & others 1985). Zygote germinates to form young sporophyte. Centrioles are inherited paternally, mitochondria and chloroplasts maternally after fertilization. Abnormal development of parthenogenetic sporophytes probably due to lack of centrioles (Motomura 1990, 1991). Sporophyte consists of different tissues: the central medulla, the parenchymatous cortex and the outer meristoderm, which is both photosynthetic and meristematic. Haptera lacks medulla. Trumpet hyphae in the medulla are sieve elements containing sieve plates with pores thereby enabling active translocation of photosynthesis products (Schmitz & Srivastava 1974, Schmitz & Lobban 1976). Mucilage canals form an interconnected system in cortex of stipes and/or blades, in some species lined by secretory cells (Kasahara 1985).

Information contributed by: I. Bartsch. The most recent alteration to this page was made on 2017-08-29 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as feminine.

Most recent taxonomic treatment adopted: Silberfeld, T., Rousseau, F. & Reviers, B. de (2014). An updated classification of brown algae (Ochrophyta, Phaeophyceae). Cryptogamie Algologie 35(2): 117-156, 1 fig., 1 table.

Comments: Life cycle in nature shows a strong seasonality in most species with rapid growth in spring and sorus formation in summer to autumn (review: Lüning 1982). There is experimental evidence that sorus formation in L. saccharina and L. setchellii and new blade formation in L. hyperborea is a photoperiodic shortday response (Lüning 1986, 1988, tom Dieck 1991). In L. setchellii acircannual growth rhythm became apparent in continuous longday conditions (tom Dieck 1991). Nutrients may modify growth, but are no trigger (Chapman & Craigie 1977). Temperature also has a direct effect on seasonal growth (Druehl & others 1987). Photosynthetic rates of L. longissima are generally highest during the colder season (Sakanishi 1991). Temperature tolerance (2 weeks exposure) of gametophytes ranges between 19 and 26_ sporophytes are normally 1-2_less tolerant and growth stops at even lower temperatures (tom Dieck 1992, 1993). Genus forms extensive sublittoral kelp beds mainly in cold-temperate waters of the N-Pacific, N and S Atlantic, but lacks in western South America, Australia and Antarctica (distribution maps: Lüning 1990). Hybridization experiments show interfertility between N Pacific and N Antlantic Simplices species but not Digitatae species (Bolton and others 1983, tom Dieck 1992). First molecular data suggest a divergence time of N Atlantic species at 15-19 Ma ago from a most recent ancestor in the N Pacific (Stam and others 1988). Genus of great economic importance as food and alginate source. Considerable harvest of natural stands in Europe and Japan. Aquaculture of Laminaria mainly in China and Japan. Total world-wide harvest is estimated at ca. 2 million wet metric tons per year (reviews: Brinkhuis and others 1987, Nisizawa and others 1987, Glicksman 1987).

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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 29 August 2017. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 09 December 2023

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