English: Cytoskeletal innovations during chromist origins. Chromists initially kept all these cytoskeletal components, modifying them as centrioles moved subapically as the text explains. Their sister clade plantae lost BB, the R2 outer branch, and B fibres. A second anterior right root R4 (not shown; see text) evolved polyphyletically by heterochrony in several chromist and plant lineages as a simplified developmental precursor of R2 (1 or few mts). The text argues that developmentally and evolutionarily the singlet root (S, brown) is a specialised R2 subcomponent, not a third posterior root as traditionally assumed. Dorsal fan and apical mts are actually longitudinal (as shown for BB only); the purple line symbolises a cross section of their mt arrays.