Prasiola, 1838, nom. cons.
Holotype species: Prasiola crispa (Lightfoot) Kützing
Original publication and holotype designation: Meneghini, G. (1838). Cenni sulla organographia e fisiologia delle alghe. Nuovi Saggi della [Cesarea] Regia Accademia di Scienze, Lettere ed Arti di Padova 4: 325-388.
Taxonomic status: currently recognized as a distinct genus.
Gender: This genus name is currently treated as feminine.
Most recent taxonomic treatment adopted: John, D.M. (2002). Order Prasiolales. 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. 473-475. Cambridge: Cambridge University Press.
Based on Ulva tribus Prasiola C. Agardh, Sp. Alg. 1: 416. 1823, but this name is invalid (Art 37.6) as Ulva tribus Prasiola C. Agardh is a misplaced term, contrary to Art. 5. - (9 Apr 2009) - M.D. Guiry
Description: Thalli forming monostromatic blades generally expanded above and narrowing to short stipitate region at base. Blade shape varies from orbicular, to irregular or spatulate to long linear; terrestrial and marine species generally 0.5 to 20 mm in high, freshwater forms usually much larger. Vegetative cells squareto rectangular, moslty alligned in distinct vertical and horizontal files, about 5-10 (-20) µm in diameter, gamete producing cells even smaller. Marginal or basal rhizoids may be present. Blades become polystromic in regions of gamete production. Spore and gamete formation occur at blade apices. Cell walls prominent, comprising up to ca. 50% of thallus volume.
Cells uninucleate with single, stellate chloroplast and prominent central pyrenoid. Cell walls mostly xylomannan.
Asexual reproduction commonly by aplanospores. In some species propagation by fragmentation or release of vegetative cells as akinetes. Some species entirely asexual with blades recycling by spores (P. furfuracea), or spores develop into aplanosporangia, the products of which regenerate the blade form (P. calophylla).
Sexual reproduction oogamous and either monoecious or dioecious with biflagellate, drop-shaped sperm 2-7 µm long, and small, non-motile, rounded to irregular shaped eggs 3-6.8 µm long; sperm only flagellated stage in life history. Sperm attachment by the absorption of one flagellum into the egg results in planozygote that settles and absorbs entire sperm cell. Zygotes grow into new diploid individuals although zygotic meiosis inferred for one species. In P. stipitata, asexual, aplanospore-producing thalli produce spores that form similar plants or develop into gamete forming blades. Zygotes may develop into either blade type. During maturation of gamete-forming thalli meiosis occurs in vegetative cells near apices and these cells continue to divide, first in plane of thallus and then in three dimensions, forming dense packets of cells. These divisions result in mosaic of male and female gametangial areas. Lighter colored cells and portions of blade produce sperm, whereas darker colored regions produce eggs. Gamete release involves dissolution of cell walls; in P. meridionalis bladder-like structure is formed in which gametes mixed. A variety of environmental cues implicated in induction of sexual reproduction. Details of life history remain problematic for many species. Chromosome numbers of n=3, 6 or 8 have been reported.
Information contributed by: D.J. Garbary & M.D. Guiry. The most recent alteration to this page was made on 18 Apr 2021 by M.D. Guiry.
Comments: Prasiola species are cosmopolitan in arctic to temperate climates in terrestrial, freshwater and marine conditions. Marine species mostly in high intertidal and adjacent splash zone habitats where they grow in great densities, often associated with bird rocks. Freshwater species in rapid streams, terrestrial forms on rock or damp soil. The supralittloral species, P. crispa, grows at salinities from 0.35-17.5 ppt. Flagellar apparatus with 9 + 1 microtubule configuration in flagellar axoneme, 180° rotational symmetry and counterclockwise absolute orientation of major components. Flagella naked with an elongated hairpoint. Some species form regular associations with the ascomycete, Kohlmeyera complicatula. These associations (mycophycobioses) usually referred to Prasiola borealis and P. tessellata in northern and southern hemispheres, respectively, however, this infection is also reported for P. crispa subsp. antarctica. This symbiosis may also be referred to as the lichen Mastodia. The taxonomic status of these entities remains unclear, i.e., are they distinct taxa or simply populations infected with the fungus?
Prasiola is the most mophologically elaborate genus in the Prasiolaceae and has the most species. Ultastructure of flagellar apparatus indicates close relationship with Rosenvingiella, which has been confirmed by sequencing.
The direction of evolution in Prasiola is thought to be into marine habitats rather than from marine to terrestrial/freshwater environment.
Numbers of names and species: There are 50 species names in the database at present, as well as 13 infraspecific names. Of the species names, 35 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.
Friedl, T. & O'Kelly, C.J. (2002). Phylogenetic relationships of green algae assigned to the genus Planophila (Chlorophyta): evidence from 18S rDNA sequence data and ultrastructure. European Journal of Phycology 37: 373-384.
Karsten, U., Friedl, T., Schumann, R., Hoyer, K. & Lembcke, S. (2005). Mycosporine-like amino acids and phylogenies in green algae: Prasiola and its relatives from the Trebouxiophyceae (Chlorophyta). Journal of Phycology 41: 557-566.
Darienko, T., Gustavs, L., Mudimu, O., Menendez, C.R., Schumann, R., Karsten, U., Friedl, T. Proschold, T. (2010). Chloroidium, a common terrestrial coccoid green alga previously assigned to Chlorella (Trebouxiophyceae, Chlorophyta). European Journal of Phycology 45(1): 79-95.
Sluiman, H.J., Guihal, C. & Mudimu, O. (2008). Assessing phylogenetic affinities and species delimitations in Klebsormidiales (Streptophyta): nuclear-encoded rDNA phylogenies and ITS secondary structure models in Klebsormidium, Hormidiella, and Entransia. Journal of Phycology 44(1): 183-195.
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: 29 December 2000 by M.D. Guiry
Verified by: 18 April 2021 by M.D. Guiry
Linking to this page: http://www.algaebase.org/search/genus/detail/?genus_id=29
Please cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 16 October 2021.