Joanna Zalewska-Gałosz

Potamogeton taxa proposed by J. F. Wolfgang and his collaborators

In the first half of 19 t h century Jan Fryderyk Wolfgang (1775-1859) was the outstanding expert on Potamogetonaceae. Twelve of the names he proposed in a manuscript of a monograph on Potamogeton were validly published bySchultes & Schultes (1827). Of these, four names are now the correct names for the respective taxa, one for a species (P. rutilus Wolfg.) and three for hybrids (P × nerviger Wolfg., P × salicifolius Wolfg. and P × undulatus Wolfg.). Ten names of Potamogeton taxa described by Wolfgang are typified in this paper, together with two names proposed by his collaborators, Besser and Gorski. The identity of these names is discussed.

Potamogeton × subrufus Hagstr.: a neglected Potamogeton hybrid

The original material of Potamogeton × subrufus Hagstr. [= P. lucens L. × P. nodosus Poir.] and the herbarium material of the morphologically most similar hybrid, P. × fluitans Roth [= P. lucens L. × P. notans L.], were examined taxonomically. Approximately 45 characters were studied on 42 herbarium specimens of both taxa. The analysis shows that P. × subrufus displays several characters consistently different from those of P. × fluitans. Two new European localities of P. × subrufus found during the study are also provided and a morphological description of the hybrid, including distinguishing characters, is given.

2597) Proposal to reject the name Potamogeton nerviger (Potamogetonaceae)

Potamogeton nerviger was described by J.F. Wolfgang (l.c.) as a species growing “In fluvio Wierzchnia circa Lelany Lithuaniae”, which is now the Verknė River near Lielionys, Lithuania. Duplicates of the original collection were widely distributed (Kaplan & Zalewska-Gałosz, l.c.) and studied by several Potamogeton experts, who interpreted its identity in various ways. Earlier authors had regarded P. nerviger as conspecific with P. alpinus Balb. (Bennett in J. Bot. 27: 243. 1889), sometimes recognizing it as infraspecific taxon P. rufescens subsp. nerviger (Wolfg.) K. Richt. (Pl. Eur. 1: 12. 1890), P. alpinus var. purpurascens subvar. nerviger (Wolfg.) Asch. & Graebn. (Syn. Mitteleur. Fl. 1: 311. 1897; Graebner in Engler, Pflanzenr. IV. 11 (Heft 31): 73. 1907) or P. alpinus var. nerviger (Wolfg.) G. Fisch. (in Mitt. Bayer. Bot. Ges. 4: 153. 1930). Fischer (in Ber. Bayer. Bot. Ges. 11: 46. 1907) suggested that it might be a hybrid between P. alpinus and P. lucens. The important monographer of Potamogeton, Hagström (in Kongl. Svenska Vetensk. Acad. Handl., ser. 2, 55(5): 149. 1916), carefully examined the original plants and considered them to be identical with the British hybrid P. ×griffithii A. Benn. (in J. Bot. 21: 65. 1883), which he considered to be P. alpinus × P. praelongus, an opinion in which he was followed by Dandy & Taylor (in J. Bot. 77: 282. 1939) and by Preston (Pondweeds Gr. Brit. Ireland: 266. 1995) in so far as the origin of P. ×griffithii was concerned. Dandy (List Brit. Vasc. Pl.: 134. 1958; in Stace, Hybrid. Fl. Brit. Isl.: 453. 1975) and Dandy & Taylor (in Watsonia 6: 315–316. 1967) followed Fischer’s view on the identity of P. ×nerviger regarding it as applying to a hybrid between P. alpinus and P. lucens, that had been discovered in western Ireland. This identity was widely adopted in later taxonomic publications and currently is almost universally accepted (e.g., Stace, New Fl. Brit. Isles: 909. 1991; Czerepanov, Sosud. Rast. Rossii Sopred. Gosud.: 805. 1995; Preston, l.c.: 260; Wiegleb & Kaplan in Folia Geobot. 33: 264. 1998; Trei & al. in Kuusk & al., Fl. Baltic Countries 3: 206. 2003; Kaplan & Zalewska-Gałosz, l.c.; Wiegleb & al. in Feddes Repert. 119: 439. 2008; Preston in Stace & al., Hybrid Fl. Brit. Isles: 325. 2015; Uotila, Euro+Med Plantbase, http://www.emplantbase.org, accessed 5 Nov 2017). However, Galinis (in Natkevičaitė-Ivanauskienė, Lietuvos TSR Flora 2: 63. 1963) interpreted P. ×nerviger as a hybrid between P. alpinus and P. gramineus (as “P. heterophyllus”). Sequencing of plants from Germany recorded as “P. ×nerviger” by Wiegleb & al. (l.c.) showed that these actually represented a slender form of P. ×salicifolius, i.e., the hybrid P. lucens × P. perfoliatus (Kaplan & Fehrer in Taxon 60: 763. 2011). Potamogeton ×nerviger was claimed to occur also in Russia by Papchenkov (Gibridy Maloizv. Vidy Vodn. Rast.: 40–41. 2007) but the actual identity of these plants is unclear. A recent combined molecular, morphological and anatomical investigation (Zalewska-Gałosz & al. in Preslia 90: 135–149. 2018) has shown that the type collection of P. ×nerviger is not P. alpinus × P. lucens, as is widely believed, but another hybrid, P. nodosus × P. perfoliatus, which had already been named P. ×assidens Z. Kaplan & al. (Zalewska-Gałosz & al. in Taxon 59: 562. 2010) and which is now known from several countries of Europe and Africa (ZalewskaGałosz & al., l.c. 2010; Kaplan & al. in Preslia 85: 447–448. 2013). As we have now shown (Zalewska-Galosz & al., l.c. 2018) that the type of P. ×assidens and that of P. ×nerviger belong to the same nothospecies (arising from P. nodosus × P. perfoliatus), under the priority rule of the International Code of Nomenclature (ICN; McNeill & al. in Regnum Veg. 154. 2012), P. ×nerviger, as the earlier validly published and legitimate name, should now replace P. ×assidens. However, the name P. ×nerviger, although published 190 years ago and well established in the literature, has never been interpreted in this sense. Consequently, this nomenclatural change would cause considerable confusion and usage of this name would be inevitably associated with ambiguity as to the actual parentage of the taxon to which it refers. It should be noted that due to their high diversity, frequent occurrence, persistence and occasional dominance in aquatic communities, Potamogeton hybrids are mostly referred by their binomials. Although hybrids may also be denoted by hybrid formulas, many Potamogeton hybrids are morphologically so well defined that they were first recognized as morphologically distinct entities and described as species without any suggestion of hybrid origin. There are also practical reasons, such as that hybrid binomials are easier to handle in databases than are formulae and encouraging the use of binomials may prevent botanists reporting hybrids that do not actually exist (see Danihelka & al. in Preslia 84: 655. 2012 for discussion on this topic). Some morphologically well-defined hybrids can even be distinguished and are known under their binomials although their exact parentages are unclear or uncertain (Kaplan & Fehrer, l.c.: 760). That is why Potamogeton hybrids are recorded under their binomials in the taxonomic literature rather than under their hybrid formulae. Replacing the taxonomically clear name P. ×assidens by the controversial name P. ×nerviger in a completely different interpretation from any accepted previously and would constitute an undesirable and disadvantageous nomenclatural change for purely formal reasons. We therefore propose rejection of the name P. nerviger under Art. 56 of the ICN.

Reinterpretation of Potamogeton ×nerviger: solving a taxonomic puzzle after two centuries

Hybrids form an important component of Potamogeton diversity but their exact taxonomic identities and distributions are often insufficiently known. Potamogeton nerviger was described from Lithuania in 1827 as a proper species. Based on morphological and anatomical characters, its interpretation has since varied, ranging from synonymization with other species to identification as different hybrids and intraspecific taxa. Currently, it is universally recognized as the hybrid P. alpinus × P. lucens. Using a combined molecular, morphological and anatomical investigation we re-examined the identity of P. ×nerviger, based on both original and recent plant material. We report a successful amplification and sequencing of nuclear ribosomal ITS1 region from a 188year-old type collection. This was shown to be genetically identical to the morphologically matching plants recently collected at the type locality. Comparison with molecular characters of the possible parental species shows that P. ×nerviger is not P. alpinus × P. lucens, as currently believed, but another hybrid, P. nodosus × P. perfoliatus, which is currently called P. ×assidens. This molecular identification is also supported by anatomical evidence. In contrast, the actual existence of the hybrid P. alpinus × P. lucens is doubtful. Consequences for nomenclature and identities of records reported from other sites are discussed.