''Crucigenia'' 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

Scenedesmaceae Scenedesmaceae is a family of green algae in the order Sphaeropleales. ''Scenedesmus'' algae are commonly found in freshwater plankton. The former family Coelastraceae is considered a synonym of Scenedesmaceae. The family has existed since at ...

. It is widespread, but not often abundant, in freshwater habitats (as

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

) around the world.

Description

''Crucigenia'' consists of colonies of four cells in a flattened square shape, up to 16 μm in diameter; occasionally these colonies may be joined together to form 8- or 16-celled compound coenobia. Colonies are embedded in a thin, gelatinous envelope. Cells are triangular, ovoid, ellipsoid, or rectangular, forming a small hole in the center of the colony. Cells are uninucleate (with a single nucleus) and with a single, parietal

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 ...

that may or may not contain a

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 ...

. Asexual reproduction occurs by the formation of

autospore Autospores are a type of spores that are produced by algae to enable asexual reproduction and spread. They are non-motile and non-Flagellated cell, flagellated Aplanospore, aplanospores that are generated within a parent cell and have the same sha ...

s; four autospores are produced within the mother cell, and are released through a tear in 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, ...

. Sexual reproduction has not been observed in this genus.

Taxonomy

''Crucigenia'' has a somewhat complex taxonomic history. It was first described by

Charles François Antoine Morren Charles François Antoine Morren (3 March 1807 in Ghent – 17 December 1858 in Liège), was a Belgian botanist and horticulturist, and Director of the ''Jardin botanique de l'Université de Liège''. Morren is credited with introducing the term " ...

in 1830 containing the type species ''C. quadrata'', but then renamed ''Staurogenia'' by

Friedrich Traugott Kützing Friedrich Traugott Kützing (8 December 1807 in Ritteburg – 9 September 1893) was a German pharmacist, botanist and phycologist. Despite his limited background in regard to higher education, Kützing made significant scientific contribution ...

without an explanation; later the name ''Crucigenia'' was noted to be the correct name. ''Crucigenia'' is similar to the genus '' Tetrastrum''. The genus ''Tetrastrum'', unlike ''Crucigenia'', may have spines or warts on its cell walls. It is also similar to the genus '' Willea'', also known by its synonym ''Crucigeniella''; in ''Willea'' the colony is overall rectangular, not square, and the hole in the center of the colony is rhomboidal. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, '' Crucigenia quadrata'' is placed in the family

, but the genus is not

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 ...

: other species, such as '' Crucigenia lauterbornii'' are phylogenetically within the order

Chlorellales The Chlorellales are an order of green algae in the class Trebouxiophyceae. The Chlorellales include mostly freshwater or terrestrial (rarely marine), coccoid algae. Molecular phylogenetic studies mostly tend to find Chlorellales to consist of t ...

. Species are distinguished from each other by the cell shape, and whether a pyrenoid is absent or present.

References

Sphaeropleales genera Sphaeropleales Freshwater algae {{Green algae-stub