Sphaeropleales is an order of green algae that used to be called Chlorococcales. The Sphaeropleales includes vegetatively non-motile unicellular, colonial , or filamentous taxa. They have biflagellate zoospores with flagella 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 walls or have only a very fine layer surrounding the cell membrane.
Phylogeny
Modern molecular phylogenetics 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.