Zygnema C., 1817, nom. et typ. cons.
Holotype species: Zygnema cruciatum (Vaucher) C.Agardh
Original publication and holotype designation: Agardh, C.A. (1817). Synopsis algarum Scandinaviae, adjecta dispositione universali algarum. pp. [i]-xl, -135. Lundae [Lund]: Ex officina Berlingiana.
Taxonomic status: currently recognized as a distinct genus.
Most recent taxonomic treatment adopted: Guiry, M.D. (2013). Taxonomy and nomenclature of the Conjugatophyceae (=Zygnematophyceae). Algae. An International Journal of Algal Research 28: 1-29.
Description: Thalli comprised of unbranched uniseriate filaments intertwined to form skeins. Cells cylindrical, 10 to 50 µm in diameter, most 20-30 µm; length equal to or several times width; cell wall two-layered with inner cellulose, outer mucilage layer; external mucilage sheath ranges from very thin to wider than cell, but generally thinner than that of related Spirogyra; end walls plane; no flagellated stages. Cells uninucleate; chloroplasts usually two (rarely four) per cell, each plastid with large pyrenoid at center of radiating short branches in stellate pattern. Nucleus in cytoplamic bridge between chloroplasts. Chromosomes (n=14 to 82) typically small, dotlike (<1.5 µm). Haploid chromosome number 14 to 82. Asexual reproduction by mitosis and fragmentation. Akinetes very common as overwintering form; aplanospores and fragments may also persist through winter. Life cycle haplobiontic, meiosis zygotic. Sexual reproduction by conjugation, most often scalariform; lateral conjugation also observed (see definitions under Spirogyra). Majority of species anisogamous ; one gamete amoeboid, the other stationary; some species isogamous (both gametes motile); zygospores forming inside one cell wall of conjugating pair (anisogamous); but many species isogamous with zygospores forming in conjugation tube between cells; in some of these zygospores are cut off from gametangia by distinct cross wall. Most species homothallic; one heterothallic species known. Chloroplast inherited from receptive (female) cell in anisogamous in few species studied. Zygospore median wall colored brown or blue; ornamention crucial in species identification. Zygospores compressed-globose to ovoid, some with keels or ridges.
Information contributed by: R.M. McCourt and R.W. Hoshaw. The most recent alteration to this page was made on 19 Oct 2015 by M.D. Guiry.
Comments: One of three commonly encountered genera in Zygnemataceae, including equally common Mougeotia and far more widespread and abundant Spirogyra. Collected from all continents, from sea-level to mountain habitats, tropical to arctic climates. Habitats range widely from quiet to running water; fresh to brackish. Filaments usually found as free-floating masses. No known economic use or nuisance problems. Fossil zygospores known from Holocene, but may have diverged from other zygnematacean genera as early as Carboniferous. Experimental uses: pyrenoid isolation; zygospores used in paleoecological studies as markers for clean, oxygen-rich, shallow stagnant, mesotrophic water in habitats subject to seasonal warming. Phylogenetic relationships to other Zygnematales unclear; conflicting phylogenetic hypotheses have postulated relation to other taxa with stellate chloroplasts, either unicells (Cylindrocystis) or filaments. Along with other Zygnematales, Zygnema member of Charophyceae and thus related to lower land plants.
Swedish: Tvestjärntrådar (Tolstoy & Österlund 2003).
Numbers of names and species: There are 360 species names in the database at present, as well as 101 infraspecific names. Of the species names, 211 have been flagged as accepted taxonomically on the basis of the listed literature under the species name. In some instances, opinions on taxonomic validity differ from author to author and users are encouraged to form their own opinion. AlgaeBase is a work in progress and should not be regarded as a definitive source only as a guide to the literature..
Names: ('C' indicates a name that is accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):
Click here to also show infraspecific names in the list below.
Verification of data
Users are responsible for verifying the accuracy of information before use, as noted on the website Content page.
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.
Created: 11 April 2002 by M.D. Guiry
Verified by: 19 October 2015 by M.D. Guiry
Linking to this page: http://algaebase.org/search/genus/detail/?genus_id=43566
Please cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 21 September 2020.