(3103) Proposal to conserve the name <i>Arabis petiolata</i> (<i>Alliaria petiolata</i>) (<i>Brassicaceae</i> / <i>Cruciferae</i>) with a conserved type

(3103) Arabis petiolata M. Bieb., Fl. Taur.-Caucas. 2: 126. 1808 [Angiosp.: Cruc.], nom. cons. prop. Typus: Herb. Clifford: 338, Erysimum No. 6 (BM barcode BM000646355), typ. cons. prop. It has recently been convincingly demonstrated by Esmailbegi & al. (in Taxon 67: 324–340. 2018) and Bayat & al. (in Plant J. 108: 1768–1785. 2021) that the widespread, weedy and often invasive, allohexaploid cytotype of the species currently known as Alliaria petiolata (M. Bieb.) Cavara & Grande (in Bull. Orto Bot. Regia Univ. Napoli 3: 418. 1913) sensu lato, which is presumably European in its origin, most probably emerged due to the ancient hybridization event(s?) between ancestral taxa with genomes similar and related to the genomes of “Alliaria petiolata” sensu stricto and Parlatoria cakiloidea Boiss. (in Ann. Sci. Nat., Bot., sér. 2, 17: 72. 1842), two extant diploid taxa restricted in their geographic ranges to the Caucasus and southwestern Asia. In response to that newly revealed phylogenetic pattern and taxonomic situation, Al-Shehbaz & al. (in Taxon 74: 467–468. 2025) proposed a possible nomenclatural solution and discussed available options as follows: “Two potential solutions exist to resolve this issue. The first is to maintain the name Alliaria for the European hexaploid equivalent to Erysimum alliaria as typified by Hedge (l.c.), adopt for it the next available non-tautonymic species synonym [species epithet – SM], and create a new generic name and two new combinations for the Caucasian species. However, this approach could introduce unnecessary nomenclatural changes and confusion. The alternative solution, which we propose, is to conserve the name Alliaria with A. petiolata as the conserved type, preserving its usage for the Caucasian species. This approach ensures maximum nomenclatural stability.” However, I disagree with the proposed solution. In fact, if the proposal by Al-Shehbaz & al. (l.c.) is accepted, the well-known and ecologically and economically important species now almost universally accepted in the genus Alliaria Matthioli & Heist. ex Fabr. (Enum.: 161. 1759) as Alliaria petiolata will have a newly coined nothogeneric or, most probably, generic name (applicable to a hybridogenous genus; see comments in Mosyakin & McNeill in Taxon 72: 461–462. 2023) and an unusual specific epithet (‘alliaria’, restored from the Linnaean name Erysimum alliaria L., Sp. Pl.: 660. 1753), as evident from the intentions of Al-Shehbaz & al. (l.c.: “Once this proposal is accepted, we will publish a new nothogeneric name [emphasis added – SM] for the European hexaploid populations initially recognized by Linnaeus (l.c.) as Erysimum alliaria, without altering the species epithet”). At the same time, the generic name Alliaria will be, rather confusingly, retained for a genus of two obscure and geographically restricted Caucasian and southeast Asian species that are almost unknown beyond their native ranges and are both of little environmental and/or virtually no economic importance: “Alliaria petiolata” diploids (which will be then called A. petiolata sensu stricto) and A. taurica (Adams) V.I. Dorof. (in Takhtajan, Konspekt Fl. Kavkaza 3: 445. 2012). If that decision is applied, then any author dealing with the Caucasian/southwestern Asian diploid Alliaria petiolata will be probably advised to explain that this name is now used in the strictest sense, excluding hexaploids to which that name was earlier most widely (mis)applied. Even if the name Alliaria petiolata was in fact misapplied to the presumably European and now widespread allohexaploid species widely known as an invasive environmental weed, that misapplication was (and still is) very consistent and systemic. This name, in that wide sense and circumscription, is accepted in many standard floras and manuals (e.g., Ball in Tutin & al., Fl. Europ. 1: 267. 1964; Kotov in Fedorov, Fl. Evropeiskoi Chasti SSSR 4: 137. 1979; Cheo & al. in Wu & Raven, Fl. China 8: 171. 2001; Al-Shehbaz in Fl. North Amer. N. Mexico 7: 745. 2010; etc.), included in numerous articles, databases and web resources (e.g., Plants of the World Online, Global Biodiversity Information Facility, Marhold in Euro+Med PlantBase, etc.; all web resources accessed 2 Apr 2025), and thus it would be highly confusing to restrict this name to an obscure Caucasian species and to coin a new generic (or nothogeneric) name and a new species-rank combination for the species most widely known as A. petiolata. The greatest importance of hexaploid “European” Alliaria petiolata (known as garlic mustard) is that it is an environmental weed in several regions of the Globe, but mostly in North America. There were definitely multiple introductions of A. petiolata to North America, from at least six European regions, but mainly from the British Isles, northern and central Europe (Durka & al. in Molec. Ecol. 14: 1697–1706. 2005); thus, the majority of invasive hexaploid plants known in North America as A. petiolata are of European but not Caucasian origin. There is even a special article in Wikipedia entitled “Garlic mustard as an invasive species”, with 33 references and several external links covering various aspects of the invasion of the species as an environmental weed, its morphology, ecology, biochemical, allelopathic and other properties (see, e.g. Durka & al. l.c.; Rodgers & al. in BioScience 58: 426–436. 2008, in BioScience 72: 521–537. 2022; Cipollini & Cipollini in J. Torrey Bot. Soc. 143: 339–348. 2016; Anderson & al. in Ecosphere 12: e03510. 2021; Blossey & al. in Ecol. Letters 24: 327–336. 2021, and references therein), etc. Moreover, a draft genome of A. petiolata as a model system for invasion genetics has been recently published (Alabi & al. G3 Genes Genomes Genetics 11: jkab339. 2021). A Google Scholar search for the word combination “Alliaria petiolata” performed on 24 April 2025 gave about 15,200 results (and more than one million results in the general Google search!), including 7320 results when combined with the word “invasive”, while searches for “Alliaria taurica” and “Alliaria brachycarpa” (the synonymic name under which the species now known as A. taurica was widely known earlier) resulted in 4 and 41 matches, respectively. That clearly illustrates which species is best associated with the generic name Alliaria. The Linnaean binomial “Erysimum alliaria” gave 362 matches, mainly because it is quite often cited in synonymy of Alliaria petiolata s.l. A Google Scholar search for the binomial “Alliaria officinalis” gave 1940 matches, which is not surprising because the binomial A. officinalis Andrz. ex M. Bieb. (Fl. Taur.-Caucas. 3: 445. 1819, nom. illeg. superfl.) was widely used as the accepted name before 1913 (and quite often even after that date; see, e.g., Busch in Komarov, Fl. URSS 8: 31. 1939; Grossh., Fl. Kavkaza, ed. 2, 4: 151. 1950; Kotov in Klokov & Visyulina, Fl. URSR 5: 214. 1953; etc.) and is still widely cited as a synonym of the currently accepted name A. petiolata. It might be possible to resurrect the name Alliaria officinalis as the accepted name for the widespread hexaploid, for example, by conserving that name, with a conserved type corresponding to the type of Erysimum alliaria L. That would also automatically link the application of the generic name Alliaria to the weedy hexaploid of presumably European origin. However, in my opinion, the resurrection of the name A. officinalis as the accepted name for the hexaploid European species now known as introduced and invasive in many regions of the globe is not the best option. Instead I propose the conservation of the basionym of Alliaria petiolata, Arabis petiolata, with a conserved type identical to the type (lectotype, designated by Hedge in Taxon 51: 533. 2002) of Erysimum alliaria L. If this proposal is accepted, (1) the generic name Alliaria will be maintained for the well-known and widely distributed allohexaploid species, thus matching both the original intended application of that generic name and the Linnaean and pre-Linnaean use of the epithet or informal name “alliaria”; (2) the species name Alliaria petiolata will be properly applied to the mentioned allohexaploid species, as it was widely or almost universally accepted during the twentieth century and the first quarter of the twenty-first century. Also, as a result of accepting the present proposal, (3) a new genus name will be most probably needed for the segregate genus of two little-known and predominantly non-weedy Caucasian and southwestern Asian species currently known as “Alliaria petiolata” (diploids) and A. taurica, and (4) a new species name will be probably needed for “Alliaria petiolata” diploids; however, some existing name(s?) may actually refer to that Caucasian species in the strict sense, e.g., Alliaria matthioli Rupr. (in Mém. Acad. Imp. Sci. Saint Pétersbourg, Sér. 7, 15(2): 85. 1869). In my opinion, a new generic name for two rather obscure Caucasian/southwest Asian species, plus (probably?) one species name for one of them, will not be an excessive price for maintaining the nomenclatural stability for a widespread, often weedy, regionally invasive and environmentally important allohexaploid species. It should be noted that new genera, Lysakia Esmailbegi & Al-Shehbaz (in Taxon 67: 334. 2018) and Mummenhoffia Esmailbegi & Al-Shehbaz (l.c.) containing one species each, have been recently established in Thlaspideae in parallel with several other generic rearrangements (see Esmailbegi & al., l.c.), so I think that adding just another generic name to house two little-known species will not disrupt much the nomenclature in the group. Thus, the proposed conservation of the name Arabis petiolata with the conserved type (instead of the current lectotype “Ex Iberia / Steven”, LE00050388, designated by Dorofeyev, l.c.: 446) corresponding to the lectotype of the Linnaean name Erysimum alliaria will best serve nomenclatural stability by preserving the current widespread application of the generic name Alliaria and the currently widely accepted name Alliaria petiolata as applied to an exceptionally important invasive environmental weed, a model species for invasion ecology. I am grateful to John H. Wiersema (Smithsonian Institution, Washington, D.C., U.S.A.) and Melanie Schori (United States Department of Agriculture, Washington, D.C., U.S.A.) for their useful comments on the manuscript.