'Unfinished' Morphogenesis Hides Different Speciation Pathways in Charophytes: Evidence from the 190-Year-Old Original Material of Chara denudata (Charales, Charophyceae)

Several Chara L. species have 'unfinished' morphogenesis that is recognizable because of their imperfect stem and branchlet cortication compared to the perfectly corticated species. Chara denudata A. Braun, described from South Africa, is one of these species, assumed for a long time to be conspecific with C. dissoluta A. Braun ex Leonhardi, as described from Central Europe. An attempt to resolve this long-lasting uncertainty in the framework of integrative taxonomy is implemented here. The restudy of the original material of both species showed similarities but did not identify a hiatus in their morphological traits, which represents evidence for their placement in the subsection Chara R.D. Wood according to morphology. Bifid adaxial bract cells, a trait rarely encountered among charophytes, were found for the first time in C. dissoluta. According to the rbcL and matK sequences, C. denudata was unexpectedly placed within the section Grovesia R.D. Wood, far from the clusters of the section Chara with C. dissoluta. This is in obvious disagreement with the position of C. denudata according to morphology. Both species were distinct according to their biology, habitat preference, and distribution and were accepted as distinct species. Therefore, the 'unfinished' morphogenesis resulting in morphological similarity hides different speciation pathways in charophytes.