A nomenclatural survey of the genus Amaranthus (Amaranthaceae) 10. What is Amaranhus commutatus?

The name Amaranthus commutatus, originally validated by Kerner for a plant taxon from Hungary and Slovakia, was studied as part of a series of contributions with the final aim to clarify the complicated nomenclature of the genus Amaranthus. On the basis of the protologue, the name Amaranthus commutatus cannot be associated with any European species, while out of Europe, Kerner's original data of A. commutatus may match the morphology of the Australian species A. rhombeus. Unfortunately, no original material has been traced so far and thus no lectotype can be designated (Arts. 9.3 and 9.4 of Shenzhen Code). Consequently, neotypification is desirable according to Art. 9.8. However no specimens of Amaranthus seen by Kerner have been traced and it was very difficult to understand Kerner's concept of that taxon. Having no suitable specimens available, I prefer to avoid the designation of a neotype, and the possible synonymization of A. commutatus with A. rhombeus based just on Kerner's data. Furthermore, the synonyms cited by Kerner in the protologue [Amaranthus blitum var. polygonoides (here lectotypified on a specimen preserved at K), and A. blitum var. prostratus (lectotype designated by Iamonico in 2016 on a Balbis' illustration] refer to other species, i.e. A. albus (new proposed synonymy) and A. deflexus, respectively. The treatment of Amaranthus commutatus appears inconsistent but this fact is not ground for rejecting of the name since does not threat any other name and there are no disadvantageous nomenclatural changes (Art. 56.1). Since the failure to properly designate a type, and the impossibility to reject A. commutatus, Kerner's name continues to be of ambiguous nature and is proposed as listed as a name incertae sedis.