Editing Euglena (section)

===Recent classification===
[[File:Euglenoid movement.jpg|thumb|left|300px|Euglenoid movement, known as [[metaboly]]]]
In 1881, [[Georg Klebs]] made a primary taxonomic distinction between green and colorless flagellate organisms, separating photosynthetic from heterotrophic euglenoids. The latter (largely colorless, shape-changing uniflagellates) were divided among the Astasiaceae and the [[Peranema]]ceae, while flexible green euglenoids were generally assigned to the genus ''Euglena''.<ref name="Pringsheim-1948">{{cite journal |doi=10.1111/j.1469-185X.1948.tb00456.x |title=Taxonomic Problems in the Euglenineae |year=1948 |last1=Pringsheim |first1=E. G. |journal=Biological Reviews |volume=23 |pages=46–61 |pmid=18901101 |issue=1|s2cid=33439406 }}</ref>

As early as 1935, it was recognized that this was an artificial grouping, however convenient.<ref>{{cite journal |doi=10.1002/jobm.19670070220 |title=F. E. Fritsch, the Structure and Reproduction of the Algae Vol. I/II. XIII und 791, XIV und 939 S., 245 und 336 Abb., 2 und 2 Karten. Cambridge 1965 (reprinted): Cambridge University Press 90 S je Band |year=2007 |last1=Schwartz |first1=Adelheid |journal=Zeitschrift für Allgemeine Mikrobiologie |volume=7 |issue=2 |pages=168–9}}</ref> In 1948, Pringsheim affirmed that the distinction between green and colorless flagellates had little taxonomic justification, although he acknowledged its practical appeal. He proposed something of a compromise, placing colorless, [[saprotrophic]] euglenoids in the genus ''Astasia'', while allowing some colorless euglenoids to share a genus with their photosynthesizing cousins, provided they had structural features that proved common ancestry. Among the green euglenoids themselves, Pringsheim recognized the close kinship of some species of ''Phacus'' and ''Lepocinclis'' with some species of ''Euglena''.<ref name="Pringsheim-1948" />

By the 1950s, when A. Hollande published a major revision of the phylum, organisms were classified by shared structural features, such as the number and type of flagella.<ref name="Linton-1999">{{cite journal |doi=10.1111/j.1550-7408.1999.tb04606.x |title=A Molecular Study of Euglenoid Phylogeny using Small Subunit rDNA |year=1999 |last1=Linton |first1=Eric W. |last2=Hittner |first2=Dana |last3=Lewandowski |first3=Carole |last4=Auld |first4=Theresa |last5=Triemer |first5=Richard E. |journal=The Journal of Eukaryotic Microbiology |volume=46 |issue=2 |pages=217–23 |pmid=10361741|s2cid=31420687 }}</ref> In the 1970s, it was hypothesized that photosynthetic euglenoids derived their chloroplasts by engulfing an algal cell and took its photosynthetic machinery. This [[secondary endosymbiosis]] hypothesis was later confirmed through molecular evidence, and it appears that the photosynthetic euglenoids are grouped into one clade.<ref name=Triemer>{{cite book |editor-first1=John D.|editor-last1=Wehr|editor-first2=Robert G.|editor-last2=Sheath|editor-first3=J. Patrick|editor-last3=Kociolek |date= 2014 |edition=2 |title= Freshwater Algae of North America: Ecology and Classification |last1= Triemer|first1=Richard E. |last2= Zakryś |first2=Bożena |chapter= Chapter 10. Photosynthetic Euglenoids |url= |location= |publisher= Elsevier Inc. |page= |isbn=978-0-12-385876-4 }}</ref> However, genetic analysis of the non-photosynthesizing euglenoid ''[[Astasia longa]]'' confirmed that this organism retains sequences of DNA inherited from an ancestor that must have had functioning chloroplasts; therefore, some once-photosynthetic lineages must have later lost the chloroplasts.<ref>{{cite journal |doi=10.1007/BF00309557 |title=Genes for components of the chloroplast translational apparatus are conserved in the reduced 73-kb plastid DNA of the nonphotosynthetic euglenoid flagellate Astasia longa |year=1994 |last1=Gockel |first1=Gabriele |last2=Hachtel |first2=Wolfgang |last3=Baier |first3=Susanne |last4=Fliss |first4=Christian |last5=Henke |first5=Mark |journal=Current Genetics |volume=26 |issue=3 |pages=256–62 |pmid=7859309|s2cid=8082617 }}</ref> Recognizing the non-monophyletic nature of the genus ''Euglena,'' Marin et al. (2003) have revised it to include certain members traditionally placed in ''Astasia'' and ''Khawkinea''.<ref name="Marin-2003" />

Throughout its taxonomic history, ''Euglena'' served as a "[[wastebasket taxon|holding bag]]" for species that did not morphologically fit into other groups. This made ''Euglena'' a heterogeneous assemblage, and made correct species identification very difficult. Some researchers proposed intra-generic groups within ''Euglena''; for example Pringsheim (1956) named five groups (Rigidae, Lentiferae, Catilliferae, Radiatae, Serpentes) based on cell shape and chloroplast morphology, while Zakryś (1986) named three subgenera (Euglena, Calliglena and Discoglena) based on chloroplast and paramylon morphology.<ref name=Schwartzbach/> However, molecular phylogenetics once again showed that these groups did not always correspond to evolutionary lineages.<ref>{{cite journal|doi=10.1099/00207713-51-3-773 |title=Phylogenetic analysis of chloroplast small-subunit rRNA genes of the genus Euglena Ehrenberg |date=2001 |last1=Milanowski |first1=R. |last2=Zakryś |first2=B. |last3=Kwiatowski |first3=J. |journal=International Journal of Systematic and Evolutionary Microbiology |volume=51 |issue=3 |pages=773–781 |pmid=11411697 }}</ref> To revise this, taxonomists have transferred species out of ''Euglena'' and into other genera, including ''Lepocinclis'',<ref name="Marin-2003" /> ''Phacus'',<ref>{{cite journal|doi=10.1016/j.protis.2010.02.002 |title=Reconstructing Euglenoid Evolutionary Relationships using Three Genes: Nuclear SSU and LSU, and Chloroplast SSU rDNA Sequences and the Description of ''Euglenaria'' gen. nov. (Euglenophyta) |date=2010 |last1=Linton |first1=Eric W. |last2=Karnkowska-Ishikawa |first2=Anna |last3=Kim |first3=Jong Im |last4=Shin |first4=Woongghi |last5=Bennett |first5=Mathew S. |last6=Kwiatowski |first6=Jan |last7=Zakryś |first7=Bożena |last8=Triemer |first8=Richard E. |journal=Protist |volume=161 |issue=4 |pages=603–619 |pmid=20434949 }}</ref> and the newly proposed genera ''[[Discoplastis]]'', ''[[Euglenaria]]'', and ''[[Euglenaformis]]''.<ref name=Schwartzbach/>