(2768) Proposal to conserve Paepalanthus, nom. cons. against the additional name, Tonina (Eriocaulaceae)

Abstract

(2768) Paepalanthus Mart. in Ann. Sci. Nat., Bot., ser. 2, 2: 28. Jul 1834 [Eriocaul.], nom. cons. Typus: P. erigeron Mart. ex Koern. (in Martius, Fl. Bras. 3(1): 390. 10 Jul 1863) (typ. cons.). (=) Tonina Aubl., Hist. Pl. Guiane 2: 856. Jun–Dec 1775, nom. rej. prop. Typus: T. fluviatilis Aubl. (=) Dupatya Vell., Fl. Flumin.: 35. 7 Sep–28 Nov 1829, nom. rej. Typus: non designatus. Paepalanthus Mart. (in Ann. Sci. Nat., Bot., ser. 2, 2: 28. 1834) is the name of a widespread genus that in the broad sense includes 477 species found in subtropical and tropical America, Africa and Madagascar (Govaerts & al., World Checklist of Vascular Plants; https://wcvp.science.kew.org, accessed 29 Jun 2020). Molecular phylogenetic studies have shown that Paepalanthus is paraphyletic with Brazilian Actinocephalus (Kórn.) Sano (in Taxon 53: 99. 2004), while the North American Lachnocaulon Kunth (Enum. Pl. 3: 497. 1841) and the widespread aquatic Tonina Aubl. (Hist. Pl. Guiane 2: 856. 1775) are embedded within it (Andrade & al. in Taxon 59: 379–388. 2010; Giulietti & al. in Rodriguésia 63: 1–19. 2012; Trovó & al. in Bot. J. Linn. Soc. 171: 225–243. 2013), but no taxonomic changes were made at the time of these phylogenetic studies. The genus was first expanded by Mabberley (Mabberley's Pl. Book. 2017), after which further combinations were made by Christenhusz & al. (Global Flora 4: 69. 2018), to make species names under those genera available for use under Paepalanthus. Paepalanthus had already been conserved against the earlier Dupatya Vell. (Giulietti & al. in Taxon 47: 743–744. 1998), but it came to our attention that the widespread, monotypic, Neotropical genus Tonina has priority. Tonina fluviatilis Aubl. is in use in the aquarium trade, but a name change would have little effect on this trade. It is likely that the name Tonina will persist at least for some time in horticulture and may in the long run be used as a common name, rather than a scientific one. Adoption of Paepalanthus fluviatilis (Aubl.) Christenh. & Byng in horticultural and ecological studies seems to be only a matter of time. Overall, the name Paepalanthus appears much more frequently in the scientific literature than Tonina, as evidenced by a Google Scholar search on 22 July 2020 for either name coupled with “Eriocaulaceae”, with more articles including the former by 1730 to 300 and article titles by 147 to 3. The name Giliberta Cothen. was also published before Paepalanthus in a relatively obscure publication (Cothenius, Disp. Veg. Meth.: 16. 1790), but in the original manuscript, a reference was made to “Touina [sic] Aubl. guian. p. 857”. Even though the spelling and page indicated were incorrect, it is unmistakably an illegitimate superfluous name, homotypic to Tonina, and thereby unavailable for use, so it need not be considered further. As an alternative to lumping these genera together, Paepalanthus could be split to maintain the genera Actinocephalus, Lachnocaulon and Tonina. Actinocephalus was originally described as a subgenus of Paepalanthus (Sano, l.c.: 99–107), with which it shares many characters, and has recently been shown not to be monophyletic (Andrino & al. in Bot. J. Linn. Soc.: boaa070. 2020 [https://doi.org/10.1093/botlinnean/boaa070]). Splitting the genus is likely to be taxonomically disruptive, as it could cause a further escalation of generic names (up to 10 new names have been suggested) that are likely to be difficult to distinguish in the field as they will be mostly based on minute technical characters. Moreover, the morphological diversity of this clade exhibits high levels of homoplasy, and concepts of the traditional subclassification of Paepalanthus are not consistent with the phylogenetic studies (Andrino & al., l.c.). This will result in recircumscription of the clades but will still leave us with Paepalanthus s.str. that lacks any synapomorphies to distinguish it from the new genera. A large number of new combinations will be required to satisfy the need to keeping the genera monophyletic, and a large number of species will not be able to be placed because they have not yet been sequenced and their morphology alone will make generic placement difficult if not impossible. In addition, recognition of multiple genera will not reflect the close relationships and similarity of these taxa. Therefore, the most stable and least disruptive option is to maintain the conserved Paepalanthus and reject Tonina against it, allowing nomenclatural stability at the genus level and paving the way to reorganise the subgeneric classification of Paepalanthus s.l. as previously conceived. MJMC, https://orcid.org/0000-0003-1398-8743 CvdB, https://orcid.org/0000-0001-5028-0686 JWB, https://orcid.org/0000-0003-2344-8126 MWC, https://orcid.org/0000-0002-9927-4938