Cosmarium Corda ex, 1848
Lectotype species: Cosmarium undulatum Corda ex Ralfs
Original publication:Ralfs, J. (1848). The British Desmidieae. pp. [i]-xxii, [i], -226, pls I-XXXV. London: Reeve, Benham & Reeve.
Type designated in Silva, P.C. (1952). A review of nomenclatural conservation in the algae from the point of view of the type method. University of California Publications in Botany 25: 241-323.
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.
Gontcharov & Melkonian (2008:1089) discuss the the selection of a lectotype: "The Index Nominum Genericorum (ING; http://botany.si.edu/ing/) recognizes C. margaritiferum as the type although in the earlier version of ING C. undulatum had been suggested (Silva, 1952). The designation of C. margaritiferum as the type is credited to Nägeli (1849, p. 114). However, Nägeli considered Cosmarium as the subgenus of Euastrum and referred to E. margaritiferum Ehr. Ehrenberg (1835) regarded his alga identical with Ursinella margaritifera Turpin (1820), so the correct citation should be Euastrum margaritiferum (Turpin) Ehr. Because the publications by Turpin and Ehrenberg were published before the starting point of desmid taxonomy (Ralfs, 1848), Nägeli's designation of the type species is invalid (ICBN, Art. 7.7). Obviously, Nägeli was not familiar with Ralfs%u2019s publication at that time, and his typification had no relation to the genus Cosmarium Corda ex Ralfs. Moreover, the alga described by Turpin is not identifiable and obviously not identical to two or likely three species illustrated by Ralfs under the name C. margaritiferum (1848, tables XVI, XXXIII; figs. 2a%u2013d, 3a, b). In contrast, the choice of C. undulatum as the type of Cosmarium was prompted by the fact that it is the most clearly known of the species included in the genus by Corda (Silva, 1952). We agree with Silva that Nägeli%u2019s typification should be rejected because it is based on an invalidly published name, and following Silva (1952), we regard C. undulatum as the type species of the genus Cosmarium." - (1 Jul 2010) - M.D. Guiry
Description: Cells solitary, tiny to large with shallow to deep median constriction (isthmus). Semicells rounded, reniform, pyramidate, quadrate with entire or undulate margin; subcircular to elongate-oval (biradiate) in apical view. Triradiate forms known in collections and cultures. Cell wall smooth with scattered pores or ornamented with small or large granules, emarginate verrucae, round or triangular pits, or short spinules. Central and marginal ornamentation differing or identical. Mucilaginous sheath, secreted through cylindrical cell wall pores, often surrounds cell. Chloroplasts one to several per semicell, axial or parietal, each with one to several pyrenoids per chloroplast. Nucleus in isthmus.
Asexual reproduction by cell division and new semicell formation (used as model for so-called Cosmarium-type desmids). Mitosis followed by cytokinesis at isthmus. Transverse septum of primary wall material msplits top become primary wall layer of new semicells. New semicells expand, bounded by primary wall, eventually reaching size and shape of parental semicell. Nucleus in new semicell during expansion; later migrates back to isthmus. After expansion complete, secondary wall with pores and wall ornamentation produced beneath primary wall. Daughter cell primary walls usually joined at apices; shed as single unit or disintegrate.
Sexual reproduction by homothallic or heterothallic conugation. Conjugating cells come together within mucilaginous envelope; semicells split at isthmus. Amoeboid gametes fuse between gametangia. Mature to zygospore spherical with short, acute or truncate spines (sometimes with furcate tips). Chloroplasts of only one mating type survive in zygospore. Karyogamy at germination followed by meiosis. Two gones (rarely one). Mating type controlled by single pair of Mendelian alleles. Recessive gene causes zygote mortality in C. turpinii. Crosses of haploid and diploid triradiate cells and normal biradiate cells with normal biradiate cells produce viable diploid and nonviable triploid zygospores. Inheritance of triradiate form non-Mendelian. Cosmarium in acidic, oligotrophic, aquatic environments. Occasionally subaerial or in basic, eutrophic water.
Information contributed by: J.F. Gerrath & M.D. Guiry. The most recent alteration to this page was made on 12 Sep 2013 by M.D. Guiry.
Comments: Cosmarium is found mainly in acidic, oligotrophic, aquatic environments. Occasionally subaerial or in basic, eutrophic waters. Several species are common with cosmopolitan distributions; others rarely collected, with very restricted distributions.
Numbers of names and species: There are 1513 species names in the database at present, as well as 2150 infraspecific names. Of the species names, 1009 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.
Hall, J.D., Karol, K.G., McCourt, R.M. & Delwiche, C.F. (2008). Phylogeny of the conjugating green algae based on chloroplast and mitochondrial nucleotide sequence data. Journal of Phycology 44: 467-477.
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: 12 September 2013 by M.D. Guiry
Linking to this page: http://www.algaebase.org/search/genus/detail/?genus_id=43526
Please cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2019. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 24 April 2019.