''Staurastrum'' is a large
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of desmids (
Desmidiaceae
The Desmidiaceae are one of four family (biology), families of Charophyta, charophyte green algae in the order (biology), order Desmidiales (desmids).See the National Center for Biotechnology Information, NCBI]webpage on Desmidiaceae Data extrac ...
), a group of
green algae
The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...
closely related to the land plants (
Embryophyta
The embryophytes () are a clade of plants, also known as Embryophyta (Plantae ''sensu strictissimo'') () or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophy ...
).
Members of this genus are microscopic and found in
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
habitats around the world.
The name ''Staurastrum'' comes from the Greek roots ''stauron'', meaning "cross", and ''astron'', meaning "star".
Description
''Staurastrum'' consists of singular cells with two identical halves, called semicells; in most species, the cell is deeply constricted at the middle, making the division between semicells clear. When viewed from the polar axis, they are biradiate (with two planes of symmetry) or pluriradiate (with more than two planes of symmetry).
Biradiate individuals have long, arm-shaped extensions (termed "processes") attached to the main body of the semicells. Pluriradiate individuals may lack these processes. The
cell wall
A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...
is either smooth, or covered with granules or spines. In each semicell there is a
chloroplast
A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
, usually located axially, with radiating lobes and/or ridges; some species have parietally located chloroplasts.
Identification
''Staurastrum'' as a genus is usually easy to identify, due to its long processes and symmetry. Some smaller species, particularly those without long processes, can be confused with ''
Cosmarium
''Cosmarium'' is a large genus of desmids (Desmidiaceae), a group of green algae closely related to the land plants (Embryophyta). Members of this genus are microscopic and found in freshwater habitats around the world.
The name ''Cosmarium'' co ...
'', but that genus has biradiate (not pluriradiate) cells and never with long processes. The smaller species may also be confused with ''
Tetraedron'' or various
xanthophyte algae, but differ in shape, ornamentation, and chloroplast morphology.
[
Although some species of ''Staurastrum'' are unmistakable, identification of species within the genus is often difficult. Important characters for identification include the degree of radiation (the number of planes of symmetry), overall shape and size of the cells, and the distribution and type of ornamentation on the cell wall. As with other genera of desmids, identification is complicated by the fact that these algae exhibit considerable phenotypic variability.][
]
Taxonomy
''Staurastrum'' is the second largest genus of desmids (after ''Cosmarium''), with about 800 species. It is the most heterogeneous desmid genus, and has been described as a wastebin taxon.monophyletic
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:
# the grouping contains its own most recent co ...
, as molecular phylogenetic studies have shown that members of the genus are dispersed across many clades; however, a "core" ''Staurastrum'' clade was resolved. The genus is still in use, because there is no known way of classifying desmids in line with their evolutionary history.[
]
Habitat and distribution
''Staurastrum'', as well as other desmid genera, live primarily in acidic lakes, ponds, and swamps with low nutrient levels. They usually live on sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
s or submerged surfaces. A number of species are characteristic of eutrophic
Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...
waters and are planktonic
Plankton are the diverse collection of organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they pro ...
.
Many species have a cosmopolitan distribution
In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...
. However, some species are restricted to a particular biogeographic realm
A biogeographic realm is the broadest biogeography, biogeographic division of Earth's land surface, based on distributional patterns of terrestrial animal, terrestrial organisms. They are subdivided into bioregions, which are further subdivid ...
.
Species
* '' S. affine''
* '' S. alternans''
* '' S. arctiscon''
* '' S. asteroideum''
* '' S. avicula''
* '' S. brachiatum''
* '' S. brachycerum''
* '' S. brebissonii''
* '' S. capitulum''
* '' S. cerastes''
* '' S. clepsydra''
* '' S. crenulatum''
* '' S. cristatum''
* '' S. cyclacanthum''
* '' S. dejectum''
* '' S. dickiei''
* '' S. dilatatum''
* '' S. dispar''
* '' S. galeatum''
* '' S. gemelliparum''
* '' S. gracile''
* '' S. hantzschii''
* '' S. hexacerum''
* '' S. hirsutum''
* '' S. iotanum''
* '' S. isthmosum''
* '' S. javanicum''
* '' S. laeve''
* '' S. lapponicum''
* '' S. lunatum''
* '' S. maamense''
* '' S. majusculum''
* '' S. margaritaceum''
* '' S. monticulosum''
* '' S. muticum''
* '' S. natator''
* '' S. omaerii''
* '' S. ophiura''
* '' S. orbiculare''
* '' S. paradoxum''
* '' S. pingue''
* '' S. polymorphum''
* '' S. pseudotetracerum''
* '' S. punctulatum''
* '' S. pyramidatum''
* '' S. quadricornutum''
* '' S. sebaldi''
* '' S. simonyi''
* ''S.'' sp. BBM-2004
* ''S.'' sp. desmid10
* ''S.'' sp. M752
* ''S.'' sp. M753
* '' S. spongiosum''
* '' S. subavicula''
* '' S. subgemmulatum''
* '' S. thunmarkii''
* '' S. tumidum''
References
External links
*
AlgaTerra database
Index Nominum Genericorum
{{Taxonbar, from=Q2334629
Desmidiaceae
Charophyta genera