Sphaeroplea C.Agardh, 1824
Lectotype species: Sphaeroplea annulina (Roth) C.Agardh
Original publication: Agardh, C.A. (1824). Systema algarum. pp. [i]-xxxvii, -312. Lundae [Lund]: Literis Berlingianis [Berling].
Type designated in: Kützing, F.T. (1843). Phycologia generalis oder Anatomie, Physiologie und Systemkunde der Tange. Mit 80 farbig gedruckten Tafeln, gezeichnet und gravirt vom Verfasser. pp. [part 1]: [i]-xxxii, -142, [part 2:] 143-458, 1, err.], pls 1-80. Leipzig: F.A. Brockhaus.
Description: Simple, free-floating, unbranched, uniseriate filaments composed of cylindrical, coenocytic cells with length 2-60 times their breadth. Cell diameter usually 10-50 um, but cells of S. africana var. crassa much larger (112-170 um diameter). Each cell with linear series of large, regularly spaced, aqueous vacuoles alternating with narrow zones of cytoplasm containing nuclei and chloroplasts. In most species a single annular chloroplast with 3-10 pyrenoids appears to occupy each cytoplasmic zone, although adjacent "chloroplasts" are often joined by delicate connections; more extensive, reticulate chloroplasts occur in some species. Pyrenoid matrix penetrated by numerous, branched, cytoplasmic channels. Nuclei of vegetative cells typically in pairs. Chromosomes tiny (<1 um) with S. annulina variously reported to have n=10, 16, 18 or 20. Cell division distinctive with each new daughter cell forming completely new cell wall within constraints of parental wall. Crosswalls (septae) between cells appear simple and thin in some species, but much thickened and elaborately lobed in others. A distinctive feature of the order are dense, cytoplasmic plugs formed from degenerate, residual units of cytoplasm isolated between septae of adjacent cells. Asexual reproduction by fragmentation of filaments. Zoospores not produced, except for questionable report in S. wilmani. Sexual reproduction typically oogamous, although anisogamy (with occasional production of large biflagellate female gametes) reported for S. soleirolii. Gametangia cylindrical, formed directly from vegetative cells with little or no modification of cell shape. Each oogonium produces numerous, large, spherical, green eggs in one to several rows. Antheridia typically borne on same filaments with oogonia and producing abundant tiny biflagellate male gametes which swarm prior to release through numerous small pores developed in antheridial cell wall. Male gametes enter oogonia through similar pores and are attracted chemotactically to eggs. Zygotes (oospores) develop following gametic fusion within oogonium and initially become invested with thin, hyaline, outer envelope termed a "primary membrane". With further development zygotes form thickened cell wall with species specific surface ornamentation, gradually turn orange-red, and ultimately are discharged from primary membrane. Zygotes represent resistant stage in life cycle and enable survival during extended periods of desiccation. Indirect evidence suggests meiosis most likely occurs in zygote prior to germination. Zygote germination typically results in four biflagellate cells, each of which settles on a substratum, loses its flagella, and elongates to form a spindle-shaped germling which develops into a mature vegetative filament. Sphaeroplea most common genus of ditypic order Sphaeropleales. Occurs in shallow, temporary, freshwater habitats subject to extended dry intervals (e.g., roadside ditches, margins of gravel pits or shallow ponds, temporarily flooded pastures, African "pans"). More often associated with calcareous conditions than with humic or acidic waters. Variable in occurrence; appearing in abundance at one time and place, then disappearing for many years. Encountered infrequently, possibly related in part to the ephemeral nature of its vegetative stage by means of which it is recognized. Distribution almost certainly more extensive than suggested by current records; known from all continents except Antarctica. Recent studies have described mitosis and cell division, vegetative ultrastructure, ultrastructural characteristics of the distinctive flagellar apparatus, the presence of appendages (cirri) on the zygote cell wall of S. fragilis, and a systematic comparison of species based on isozyme analyses.
Information contributed by: L.R. Hoffman. The most recent alteration to this page was made on 2021-09-06 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: Tsarenko, P.M. (2011). Sphaeropleales. In: Algae of Ukraine: diversity, nomenclature, taxonomy, ecology and geography. Volume 3: Chlorophyta. (Tsarenko, P.M., Wasser, S.P. & Nevo, E. Eds), pp. 280-355. Ruggell: A.R.A. Gantner Verlag K.-G..
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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.
Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=43480
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 06 September 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 31 January 2023