Sphaeropleales is an order of

green alga 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 ( ...

e that used to be called

Chlorococcales Chlorococcales is a formerly recognized Order (biology), order of green algae in the Class (biology), class Chlorophyceae. , the type family Chlorococcaceae was placed in the order Chlamydomonadales. Conventionally, many groups of coccoid green ...

. The order includes some of the most common freshwater

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic algae such as '' Scenedesmus'' and '' Pediastrum''. The Sphaeropleales includes vegetatively non-motile unicellular, colonial , or filamentous taxa. They have biflagellate zoospores with

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

that are directly opposed in direction (the DO arrangement): '' Sphaeroplea'', '' Atractomorpha'', '' Neochloris'', '' Hydrodictyon'', and '' Pediastrum''. All of these taxa have basal body core connections. Motile cells generally lack

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, ...

s or have only a very fine layer surrounding the

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

. Other common characteristics include a robust vegetative

, cup-shaped

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 ...

s with large pyrenoids, and relatively large nuclei. With an increase in the number of taxa for which sequence data are available, there is evidence of an expanded DO clade that includes additional zoosporic ('' Bracteacoccus'', '' Schroederia'') and some strictly autosporic genera such as '' Ankistrodesmus'', '' Scenedesmus'', '' Selenastrum'', and '' Monoraphidium''. The filamentous '' Microspora'' has been allied with the coccoid genus ''Bracteacoccus'' based on molecular data. Monophyly of the DO clade is supported by phylogenetic analysis of multi-gene data.

Phylogeny

Modern

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

s suggest the following relationships (not all families are included): Taxonomists have had difficulties classifying Characiaceae and Microsporaceae using molecular genetics, because the taxonomic affiliations of the type species are unclear. At least some of their taxa are known to related to genera within Sphaeropleales, but others are not. Additionally, the placement of the type family, Sphaeropleaceae, is problematic because some phylogenetic analyses find the family to be unrelated to the rest of the order.

References

{{Taxonbar, from=Q5357568 Chlorophyta orders