Ulothrix Kützing, 1833

Holotype species: Ulothrix tenuissima Kützing

Original publication: Kützing, F.T. (1833). Algologische Mittheilungen. Flora 16(35): 513-521, no figs.

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Type designated in: Hazen, T.E. (1902). The Ulothricaceae and Chaetophoraceae of the United States. Memoirs of the Torrey Botanical Club 11(2): 135-250, plates 20-42.

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Description: Filaments flaccid, basically unbranched and uniseriate. Cells always closely adherent. H-pieces, if present, shaped like cuffs wrapping transverse walls. Cell wall in juveniles thin and smooth, later more thickened and sometimes roughened. Apical cell rounded, seldom slightly narrowed. Attachment by simple or rhizoidal basal cells, sometimes by rhizoidal outgrowths projecting from both intercalary and apical cells. Cells cylindrical, sometimes dolioform, uninucleate. Juveniles with length/width ratio generally large, in older cells small. Chloroplast single, parietal, girdle-shaped, partially or fully encircling cell circumference, usually lobed and not enclosed in young cells, usually more irregular and sometimes fully closed in mature cells. Pyrenoids single, in more mature cells, surrounded by a thin or more conspicuous starch envelope; older cells accumulating starch, oil-like and volutine globules. Asexual reproduction by quadriflagellate zoospores, arising in each cell (except basal cell and cells from which rhizoids project), produced more than one per cell. Zoospores positively phototactic, oval to (sub)pyriform, enclosing a cup-shaped parietal chloroplast with distinct stigma. Aplanospores formed during arrested zoosporogenesis germinate in parental cell or after release by filament decay. Vegetative reproduction by filament fragmentation. Under adverse conditions sometimes developing thick-walled filaments with an akinete-like phase, rarely true akinetes. Sexual reproduction by isogamous biflagellate gametes, arising in all except differentiated cells. Fusion monoecious or dioecious. Filaments with gametes often coiled and yellowish-green. Gametes, more than one per cell, spindle-shaped, with cup-shaped parietal chloroplast and (in)conspicuous stigma, basically positively phototactic. Zygote negatively phototactic, after quiescence forming unicellular, stalked or sessile, (sub)globular, (sub)clavate or (sub)pyriform sporophyte, when mature producing more than 4 quadriflagellate zoospores. Life history basically heteromorphic and diplobiontic with multicellular filamentous gametophyte and unicellular Codiolum-stage sporophyte. Ulothrix cosmopolitan with wide ecological distribution especially in temperate and colder regions; usually forming strands several cm in length with extensive populations forming tufts or mats of varying size, often in green belt with distinct seasonality. Present in aerated freshwater localities such as shores of eutrophic lakes, banks of brooks, canals and rivers; less abundant in stagnant waters such as ditches and pools, and almost absent in boggy habitats. Ulothrix also flourishes in brackish areas with extreme (daily) variation in environmental factors, e.g. near mouth of intertidal freshwater streams where plants are covered with seawater at high tide, in estuaries or tidal rivers, in supralittoral pools of rocky shores, and supralittoral pools exposed to freshwater drip. In marine habitats forming extensive sheets in upper fringe of littoral zone; in mid and low littoral zone of rocky shores often present as important component of pioneer vegetation. Ulothrix grows on hard substrata, also abundant in salt marshes on soft bottoms. Early history of Ulothrix had numerous taxonomic revisions. Extensive comparative studies based on field, culture, herbarium and ultrastructural studies show 12 Ulothrix species in western Europe. Different life history patterns reported in marine species with both isomorphic and anisomorphic alternation of generation, or only an asexual filamentous phase. No consencus present regarding existence of diplobiontic life cycle, and development of zygote into so-called unicellular sporophyte questioned. Whether diplobiotic life history present or not, meiosis generally inferred as zygotic, although convincing cytological and/or genetic confirmation lacking. Not only alternation of generations may be variable, but also rate of production of (a)sexual reproductive cells, as in the brackish-water Ulothrix implexa. When invading freshwater habitats it looses capacity to produce gametes, while slowing asexual reproduction, if it occurs at all. In Ulothrix zonata light, temperature and photoperiod are factors controlling reproduction. Extensive ultrastructural studies on flagellar root systems and on mitosis and cytokinesis show Ulothrix in Ulvophyceae. Combined immunofluorescence and TEM observations indicate septum formation in Ulothrix palusalsa associated with often ill-defined microtubules. Some freshwater species, formerly placed in Ulothrix, were transferred to Uronema in Chlorophyceae based on ultrastructural evidence. Pyrenoid ultrastructure supports recent classification of Ulothrix, especially problematic freshwater species with cell diameters 3.5 to 12.6 um. Cytological studies in some species (e.g. Ulothrix zonata) show chromosome numbers of n=5-14.

Information contributed by: G.M. Lokhorst. The most recent alteration to this page was made on 2021-08-26 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: John, D.M. (2002). Orders Chaetophorales, Klebshormidiales, Microsporales, Ulotrichales. In: The Freshwater Algal Flora of the British Isles. An identification guide to freshwater and terrestrial algae. (John, D.M., Whitton, B.A. & Brook, A.J. Eds), pp. 433-468. Cambridge: Cambridge University Press.

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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
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 26 August 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 18 April 2024

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