(2932) Proposal to reject the name <i>Callitriche foliosa</i> (<i>Plantaginaceae</i>)

(2932) Callitriche foliosa Raf. in Med. Repos., ser. 2, 5: 354. Mai 1808 [Angiosp.: Callitrich. / Plantagin.], nom. rej. prop. Lectotypus (hic designatus): [U.S.A., New York or Vermont], “ad ripam meridionalem Lacûs Champlain”, Michaux (P barcode P00322496!). 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 foliosa Raf. (in Med. Repos., ser. 2, 5: 354. 1808) was validly published through the statement “C. autumnalis of do”, referring to the treatment of C. autumnalis 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. foliosa depends on an investigation of Michaux's (l.c.) treatment of C. autumnalis. Michaux (l.c.) did express doubt regarding the identity of the species in question, by the use of a question mark (“autumnalis?”). He provided scant morphological information (“foliis omnibus linearibus, emarginatis, approximatis”) and provenance as “ad ripam meridionalem lacus Champlain”. Lake Champlain is located between the American states of New York and Vermont, just extending into the southern part of the Canadian province of Québec. He also admitted that he did not see flowers of the species (“Florentem non vidi”). No specimens or illustrations were cited. Callitriche autumnalis L. is a synonym of C. hermaphroditica L. (Cent. Pl. 1: 31. 1755), a common species widely distributed in temperate and boreal areas in the Northern Hemisphere (Fassett in Rhodora 53: 215–219, t. 1175[24]. 1951; Lansdown, Callitriche Eur.: 124–130. 2008; Hassemer & Lansdown in Phytotaxa 547: 296, 298. 2022). It should be noted that, despite C. autumnalis having frequently been considered a superfluous and illegitimate name (e.g., Jarvis, Order out of Chaos: 375–376. 2007), the phrase-name of C. autumnalis (“foliis omnibus linearibus apice bifidis, floribus hermaphroditis”) is not exactly the same as that of C. hermaphroditica (“foliis omnibus linearibus, apice bifidis”); hence, C. autumnalis is not an illegitimate name (Art. 52.3 of the ICN; Turland & al. in Regnum Veg. 159. 2018). Nevertheless, despite the fact that Michaux determined (although with doubts) as C. autumnalis the element upon which Rafinesque based his C. foliosa, the latter name should not be uncritically linked to C. hermaphroditica, because the names C. foliosa and C. autumnalis are not homotypic, and especially because, as explained above, Michaux himself expressed doubt regarding the identity of the plants he called C. autumnalis. The morphological information provided by Michaux (l.c.) for his “Callitriche autumnalis?” is far from sufficient to link the entity to a single species. However, we have been able to locate a specimen (P00322496), originally from the Michaux Herbarium, which is unquestionably original material for the name C. foliosa. This sheet has three plants mounted on it, all morphologically uniform, seemingly belonging to the same population. Unfortunately, none of them has mature fruits, which would be necessary to identify those plants to species rank. In the absence of any other extant element (specimens or illustrations; see Art. 9.4 of the ICN) of original material, we designate here this specimen as lectotype of the name C. foliosa, in accordance to Art. 9.3 and 9.12 of the ICN. Based on careful study of the lectotype, we were able to narrow down the possibilities regarding the identity of the name Callitriche foliosa to the following three species: C. fassettii Schotsman (in Acta Bot. Neerl. 15: 477–483. 1966), C. hermaphroditica and C. stenoptera Lansdown (in Novon 19: 367–369. 2009). Unfortunately, it is impossible to narrow it down further, because of the absence of mature fruits in the lectotype. However, considering the geographical information provided in Michaux (l.c.) (i.e., southern shores of Lake Champlain), it is less likely that the lectotype of C. foliosa could belong to C. fassettii, as the latter species is only recorded in more western American states, namely California, Oregon and Nebraska (Lansdown, l.c. 2009: 365–366; Lansdown in FNA Ed. Comm., Fl. N. Amer. N. Mexico 17: 49–54. 2019). The other two species (i.e., C. hermaphroditica and C. stenoptera) occur in the area of Lake Champlain or in nearby areas. Our taxonomic analysis shows, therefore, that the name Callitriche foliosa could possibly be applied to any of the species listed above. Since the lectotype is insufficient for unequivocal determination at the species rank, the name C. foliosa could possibly be epitypified with a specimen belonging to any of those species (see Art. 9.9 of the ICN). Such a typification would not be in conflict with its protologue, and thus would need to be accepted. In this way, the name C. foliosa could become the correct name for the species currently called C. fassettii or C. stenoptera because the name C. foliosa predates both names. However, substituting any Callitriche name in current usage with an obscure name published by Rafinesque would be undesirable and evidently disadvantageous to nomenclatural stability. The name C. foliosa 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). By contrast, the names C. fassettii and C. stenoptera have unequivocal identities and are species names currently accepted (e.g., Lansdown, l.c. 2009: 364–369; Lansdown, l.c. 2019). Thus, 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. foliosa is here proposed for rejection. It will most likely remain impossible to ascertain the identity of C. foliosa and we consider it more appropriate to have this name rejected than arbitrarily to propose its epitypification by an element identifiable as the earlier C. hermaphroditica. Acceptance of this proposal would allow Callitriche fassettii and C. stenoptera to continue to be used as the correct names for these species, without threat from an arbitrary application or epitypification of C. foliosa. Rejection of this proposal would mean that C. foliosa could eventually replace C. fassettii or C. stenoptera as the correct name for either species. 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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