Ulva Linnaeus, 1753, nom. et typ. cons.

Holotype species: Ulva lactuca Linnaeus

Original publication and holotype designation: Linnaeus, C. (1753). Species plantarum, exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas. Vol. 2 pp. [i], 561-1200, [1-30, index], [i, err.]. Holmiae [Stockholm]: Impensis Laurentii Salvii.

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Description: Mature thallus a flattened distromatic blade in which the two cell layers are developmentally independent but closely adherent. Blades can be broadly expanded, irregularly lobed, cuneate, linear, lanceolate, oblanceolate, or deeply divided into linear lacinae. Some species show regular perforations such as U. reticulata, or marginal dentations such as U. rigida, U. scandinavica and U. taeniata. Growth of blade by diffuse cell divisions primarily along the margins. Usually attached to substrate by rhizoidal cells in a basal holdfast and/or rhizoidal extensions of cells in the lower portion of the blade or occasionally extending along part or the entire longitudinal axis of the blade. Rhizoidal extensions running between the two cell layers of the blade. Vegetative cells with a single parietal chloroplast and 1 or more pyrenoids. Vegetative cells uninucleate, rhizoidal cells often multinucleate. Chromosome counts range between 5 and 13 chromosomes in the haploid thallus, with the most common number being 10. Vegetative reproduction by fragmentation or by growth of new upright thalli from basal cells and/or persistant holdfasts. Life history typically an alternation of isomorphic, unisexual haploid gametophytes and diploid sporophyte. Meiosis shown to occur during sporogenesis. With the exception of rhizoidal cells and some basal cells, all cells of the blade capable of becoming reproductive. Asexual reproduction by quadriflagellated zoospores; sexual reproduction by biflagellated anisogamous, or rarely isogamous gametes. Swarmers released from mother cells one at a time through a pore on the surface of the blade. Gametes positively phototactic; after syngamy motile zygotes become negatively phototactic. Zoospores initially positively phototactic, later becoming negatively phototactic. Germination usually direct, but a germination tube can develop prior to cell division in some species such as U. arasakii and U. californica. Germling differentiates into a uniseriate filament attached by a basal disk usually composed of primary attaching cells and rhizoidal extensions of cells in lower region of filament. In a few species a basal disk develops prior to development of the upright filament. The upright filament later becomes pluriseriate by repeated longitudinal cell divisions perpendicular to the surface of the filament. Separation of cells along the longitudinal axis lead to the development of a tubular monostromatic germling. The tube eventually becomes compressed with the walls adhering to form a distromatic blade. Extensive genetic analysis of Ulva mutabilis and other species has demonstrated a wide range of life history variations in which the reproductive and cytological cycles do not always coincide. Gametes can develop parthenogenetically into haploid gametophytes, haploid sporophytes, diploid sporophytes or sporophytes that are partially haploid and diploid. Asexual populations that reproduce by biflagellated swarmers reported from some areas may result when conditions favor parthenogenetic over sexual reproduction. A cosmopolitan genus with species in all oceans and estuaries of the world. Species of Ulva have traditionally been based on morphological, anatomical and cytological characteristics such as shape, size, presence or absence of dentation, thickness, cell dimensions and number of pyrenoids. Many studies have shown that these characteristics can be highly variable within species, varying with age, reproductive state, wave exposure, tidal factors, temperature, salinity, light and biological factors such as grazing. In recent years developmental patterns in culture, reproductive details and the apparent inability of species to interbreed have been used to evaluate species concepts based on morphological and anatomical characteristics.

Information contributed by: C. Tanner. The most recent alteration to this page was made on 2024-04-04 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.

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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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Citing AlgaeBase
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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 04 April 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 18 June 2024

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