''Monactinus'' is a

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 ...

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 ...

in the family

Hydrodictyaceae Hydrodictyaceae is a family of green algae in the order Sphaeropleales. They are found in freshwater habitats worldwide. Members of this family are either unicellular or colonial. Cells are cylindrical, polyhedral, spherical, or sometimes nearly ...

. It is very common in freshwater regions throughout the world.

Description

''Monactinus'' forms flat colonies, termed coenobia, of cells in powers of two, usually four, eight, or 16. Coenobia are disc-shaped in outline, and marginal cells are drawn out into one lobe or point. This distinguishes it from ''

Pediastrum ''Pediastrum'' is a genus of green algae, in the family Hydrodictyaceae. It is a photoautotrophic, nonmotile coenobial green alga that inhabits freshwater environments. The name ''Pediastrum'' comes from the Greek root words ''pedion'', meaning ...

'' and closely related genera, which have marginal cells which are drawn out into two lobes or points. ''Monactinus'' shows a considerable amount of morphological diversity, with cells displaying different shapes, cell wall surface granulations, and inter-cellular gaps (or lack thereof). Cells have one

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 ...

filling the cell, each with a single

pyrenoid Pyrenoids are sub-cellular phase-separated micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. ''An ...

Taxonomy

Although ''Monactinus'' was first described by

August Carl Joseph Corda August Carl Joseph Corda (15 November 1809 – 1849) was a physician, botanist, and mycologist from Bohemia. This botanist is denoted by the List of botanists by author abbreviation, author abbreviation Corda when Author citation (botany), citing ...

in 1839, for most of its history it was considered to be a synonym of ''

''. In 2005,

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 ...

analyses showed that ''Pediastrum'' ''

sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...

'' was

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

with respect to ''

Hydrodictyon The water net (genus ''Hydrodictyon'') is a taxon of freshwater green algae in the family Hydrodictyaceae. ''Hydrodictyon'' does well in clean, eutrophic water, and has become a nuisance in New Zealand, where it has been recently introduced. The ...

''. Therefore, ''Pediastrum'' was split up into several genera, including ''Monactinus''.

References

Sphaeropleales genera Sphaeropleales Freshwater algae {{Chlorophyceae-stub