Nitella sonderi A.Braun (Charales, Charophyceae) – a new record for South America, and first record from outside Australia

Nitella sonderi A.Braun is newly reported from the Patagonian Plateau, Argentina. This species was only reliably known from Australia until now. The morphological and genetic studies carried out here found no difference between Argentinian and Australian specimens. The species is dioecious, mucous-bearing on fertile whorls, with two to three-forked homeoclemous, macrodactylous branchlets with a long primary ray, an evident central secondary ray, bicellulate dactyls with a shortly narrowing tip of the penultimate cell, which is confluent with a small discoloured conical cell and large antheridia. Although only male plants were found in Patagonia, this combination of traits allowed its differentiation from other species of Nitella C.Agardh known from South America, but pointed towards the similarity with N. papillata F.S.Han & W.Q.Chen found only in South-East China. Nitella sonderi is the first dioecious species from the section Gioallenia R.D.Wood found in South America. Additions to the description of N. sonderi were suggested here based on specimens from Argentina and Australia. Doubt concerning a species record of N. morongii Allen for Australia published elsewhere was outlined. The new species record for South America highlights an unexpected biogeographical pattern, rare for dioecious species, or may suggest a case of invasion. Future taxonomic research is desirable to clarify the affinity of N. sonderi and N. papillata.