(2933) Proposal to reject the name <i>Callitriche spuria</i> (<i>Plantaginaceae</i>)

(2933) Callitriche spuria Raf. in Med. Repos., ser. 2, 5: 354. Mai 1808 [Angiosp.: Callitrich. / Plantagin.], nom. rej. prop. Lectotypus (hic designatus): “in Americâ Septentrionali, Ubiq. a Canadâ ad Carolinam”, Michaux (P barcode P00322495!). This proposal is part of a complete revision of the Callitriche L. names published or treated by Constantine Samuel Rafinesque (1783–1840) (Hassemer & Lansdown, in prep.). Callitriche spuria Raf. (in Med. Repos., ser. 2, 5: 354. 1808) was validly published through the statement “which is the call. verna of Mich.”, referring to the treatment of C. verna L. (Fl. Suec., ed. 2: 2. 1755) in Michaux (Fl. Bor.-Amer. 1: 2. 1803). Since no further information was provided by Rafinesque in the protologue, the determination of the identity of the name C. spuria is dependent on the information provided in Michaux's (l.c.) treatment of C. verna. For his “Callitriche verna”, Michaux (l.c.) provided scant morphological information (“foliis superioribus spathulato-obovalibus; inferioribus linearibus: floribus omnibus hermaphroditis”) and provenance as “ubique a Canada ad Carolinam”. No specimens or illustrations were cited. It should be noted that Callitriche verna is a legitimate, heterotypic synonym of C. palustris L. (Sp. Pl.: 969. 1753), a common species very widely distributed in subtropical to boreal areas in the Northern Hemisphere (Lansdown & Jarvis in Taxon 53: 169–172. 2004; Lansdown in Watsonia 26: 110–111. 2006; Lansdown in Novon 16: 357–360. 2006; Lansdown, Callitriche Eur.: 124–130. 2008; Hassemer & Lansdown in Phytotaxa 547: 298. 2022). Nevertheless, despite the fact that Michaux determined as C. verna the element upon which Rafinesque described his C. spuria, the latter name should not be uncritically linked to C. palustris because the names C. spuria and C. verna are not homotypic, and it is possible that Michaux erred when he determined the North American plants in question as C. verna. The morphological information provided by Michaux (l.c.) for his “Callitriche verna” is insufficient to link the entity to a single species. However, we have been able to locate a specimen (P00322495), originally from the Michaux Herbarium, which is unquestionably original material for the name C. spuria. This sheet has nine plants mounted on it, morphologically considerably uniform, seemingly belonging to the same population. In the absence of any other extant element (specimens or illustrations; see Art. 9.4 of the ICN; Turland & al. in Regnum Veg. 159. 2018) of original material, we designate here this specimen as lectotype of the name C. spuria, in accordance to Art. 9.3 and 9.12 of the ICN. The specimen P00322495 belongs to Callitriche heterophylla Pursh (Fl. Amer. Sept. 1: 3. 1813), a very common and widely distributed species in the Americas, particularly in North America (Fassett in Rhodora 53: 172–182, t. 1168. 1951; Deschamp & Cooke in Amer. J. Bot. 72: 1377–1387. 1985; Lansdown & Hassemer in Phytotaxa 501: 98–99, fig. 1[k]. 2021). It should be noted that the name C. spuria precedes C. heterophylla by five years, thus having priority as the correct name for the species. However, adoption of Callitriche spuria as the correct name for the species currently called C. heterophylla would be extremely disruptive to nomenclatural stability. The name C. spuria has not been used in the taxonomic literature other than in the protologue (Rafinesque, l.c. 1808) and a subsequent mention by Rafinesque (in Med. Repos., ser. 3, 2: 408. 1811). Callitriche spuria is presented as an “unplaced name” in Plants of the World Online (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:430044-1). By contrast, the name C. heterophylla has an unequivocal identity and has been consistently accepted as the correct name for the species in question since 1813 (e.g., Pursh, l.c.; Engelmann in Gray, Manual, ed. 5: 429. 1867; Small, Fl. S.E. U.S., ed. 2: 723. 1913; Fassett, l.c.; Bacigalupo in Darwiniana 22: 384–385, fig. 3[a–i]. 1979; Deschamp & Cooke, l.c.; Sheath & al. in Hydrobiologia 140: 183–191. 1986; Philbrick in Hickman, Jepson Man.: 458. 1993; Rolfsmeier & al. in Trans. Nebraska Acad. Sci. 25: 15–22. 1999; Philbrick & Les in Aquatic Bot. 68: 123–141. 2000; Kelly & Cooke in Amer. J. Bot. 90: 1131–1143. 2003; Lansdown in Novon 19: 364–365. 2009; Ramos & al. in Revista Ci. Desarrollo 4: 73–82. 2013; Alexander in Calochortiana 3: 94. 2016; Lansdown in FNA Ed. Comm., Fl. N. Amer. N. Mexico 17: 49–54. 2019; Lansdown & Hassemer, l.c.). Therefore, with the objective of preventing a nomenclatural change that would be evidently disadvantageous to nomenclatural stability, and in accordance with Art. 56 of the ICN, the name C. spuria is here proposed for rejection. Acceptance of this proposal would allow Callitriche heterophylla to continue to be used as the correct name for this species. Rejection of this proposal would mean that C. spuria would have to replace C. heterophylla. GH, https://orcid.org/0000-0003-4365-6934 RVL, https://orcid.org/0000-0003-0984-4552 We are grateful to Cécile Aupic (Muséum National d'Histoire Naturelle) for her help with access to specimens, and to John McNeill (Royal Botanic Garden, Edinburgh) for improving this proposal.

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