Phacus is a genus of unicellularprotists, of the phylumEuglenozoa (also known as Euglenophyta). They are light-green and are commonly found in freshwater pools, propelling themselves by gyrating their bodies. They have a single flagellum which is often as long as the Phacus' body. Euglenid, with plastids, rigid, flattened cells, most species very flat and leaf-shaped, often with ridges, folds or grooves running helically or longitudinally, giving an irregular or triradiate cross-section; many species with a long posterior spine, many twisted, flagella, eyespot and flagellar swelling as in Euglena; chloroplasts usually small, discoid, numerous, without pyrenoids; a few species (e.g. P. splendens) have large flat chloroplasts with pyrenoids; paramylon is typically deposited as a few large granules (often rings) together with many small ones; canal opening subapical; no cysts palmelloid stages rare; speciose, contemporary studies indicate that the genus is not monophyletic or holophyletic; type species: P. longicauda (Ehrenberg, 1833) Dujardin, 1841.. Species under the genus include Phacus brevisulca, Phacus claviformis, Phacus hordeiformis, Phacus longisulca, Phacus minimus, Phacus paraorbicularis, Phacus orbicularis and Phacus viridioryza.
Kosmala, Sylwia; Bereza, Magdalena; Milanowski, Rafal; Kwiatowski, Jan; Zakrys, Bozena (October 2007). "Morphological and molecular examination of relationships and epitype establishment of Phacus pleuronectes, Phacus orbicularis, and Phacus hamelii". Journal of Phycology. 43 (5): 1071–1082. doi:10.1111/j.1529-8817.2007.00386.x.
Pereira, MJ; Azeiteiro, UMM (May 2003). "Ecological notes on the species of Phacus Dujardin (Euglenophyta) from the central region of Portugal". Acta Oecologica. 24 (Supplement 1): S33–S48. doi:10.1016/S1146-609X(03)00006-7.
Su, H M; Won, L J; Ho, G Y (27 September 2013). "Bacterial mixture useful for controlling proliferation of harmful algae including Microcystis, Anabaena, Aphanizomenon, Phacus, Euglena, Peridinium, Cyclotella, Chlamydomonas and Rhodomonas, comprises Lactobacillus and Lactococcus". KR2013009902-A ; KR1311837-B1.|access-date= requires |url= (help)