biostudies-literatureUnknown8Keller A<h4>Background</h4>Within Chlorophyceae the ITS2 secondary structure shows an unbranched helix I, except for the 'Hydrodictyon' and the 'Scenedesmus' clade having a ramified first helix. The latter two are classified within the Sphaeropleales, characterised by directly opposed basal bodies in their flagellar apparatuses (DO-group). Previous studies could not resolve the taxonomic position of the 'Sphaeroplea' clade within the Chlorophyceae without ambiguity and two pivotal questions remain open: (1) Is the DO-group monophyletic and (2) is a branched helix I an apomorphic feature of the DO-group? In the present study we analysed the secondary structure of three newly obtained ITS2 sequences classified within the 'Sphaeroplea' clade and resolved sphaeroplealean relationships by applying diffBMC evolutionary biology218https://www.ebi.ac.uk/biostudies/studies/S-EPMC2519086biostudies-literatureITS2 data corroborate a monophyletic chlorophycean DO-group (Sphaeropleales).PMC2519086Keller ASchleicher TForster FRuderisch BDandekar TMuller TWolf MfalseITS2 data corroborate a monophyletic chlorophycean DO-group (Sphaeropleales).<h4>Background</h4>Within Chlorophyceae the ITS2 secondary structure shows an unbranched helix I, except for the 'Hydrodictyon' and the 'Scenedesmus' clade having a ramified first helix. The latter two are classified within the Sphaeropleales, characterised by directly opposed basal bodies in their flagellar apparatuses (DO-group). Previous studies could not resolve the taxonomic position of the 'Sphaeroplea' clade within the Chlorophyceae without ambiguity and two pivotal questions remain open: (1) Is the DO-group monophyletic and (2) is a branched helix I an apomorphic feature of the DO-group? In the present study we analysed the secondary structure of three newly obtained ITS2 sequences classified within the 'Sphaeroplea' clade and resolved sphaeroplealean relationships by applying diff2008-01-01T00:00:00Z2008 Jul2025-04-04T19:31:13.272Z2019-03-27T00:16:16ZS-EPMC25190861865569810.1186/1471-2148-8-218