(2996) Proposal to conserve the name <i>Acorus calamus</i> var. <i>americanus</i> (<i>A. americanus</i>) (<i>Acoraceae</i>) with a conserved type

(2996) Acorus americanus (Raf.) Raf., New Fl. 1: 57. Dec 1836 ≡ A. calamus var. americanus Raf., Med. Fl. 1: 25. 11 Jan 1828 [Angiosp.: Ar. / Acor.], nom. cons. prop. Typus: [U.S.A.], Maine, Penobscot Co., Orono, Basin Frog Pond, 13 Jul 1942, Ogden & Steinmetz 2473 [Pl. Exs. Grayanae No. 1216 p.p.] (CM No. 313477 [barcode 0005] [excl. ripe fruits in envelope]; isotypi [all excl. ripe fruits in envelopes]: CLEMS No. 02071 [barcode CLEMS0075920], F No. 1595485 [barcode V0462365F], FLAS No. 72248, GH barcode 01010595, IND No. 97395 [barcode IND-0008301], LE barcode LE 01249870, MICH barcode 1207514, MUHW barcode MUHW026899, NO barcode NO 0038632, US No. 1925737 [barcode 03816883], P barcode P02087753, WIS barcode v 0397276 WIS), typ. cons. prop. The species of Acorus have strong practical uses, especially in herbal medicine, pharmacology, as a source of compounds of insecticidal activity, but also in the perfume industry, as a food flavour and, historically, for candies (Buell in Rhodora 37: 367–369. 1935; Motley in Econ. Bot. 48: 397–412. 1994; Yao & al. in Insect Sci. 15: 229–236. 2008; Balakumbahan & al. in J. Med. Pl. Res. 4: 2740–2745. 2010; Rajput & al. in Phytomedicine 21: 268–276. 2014; He & al. in Phytochemistry 210: e113626. 2023). As Acorus is inferred to be a sister group to all other extant monocots, its species are of key importance for studies of early monocot evolution at morphological, genetic, and genomic levels (Rudall & Furness in Int. J. Pl. Sci. 158: 640–651. 1997; Buzgo & Endress in Int. J. Pl. Sci. 161: 23–41. 2000; Shi & al. in Nature Plants 8: 764–777. 2022; Guo & al. in Nature Commun. 14: e3662. 2023; Ma & al. in Nature Commun. 14: e3661. 2023). Despite the extensive taxonomic research, the nomenclature of Acorus has been approached only recently because of the obscurity of the original material of many historical names. The earliest legitimate species names have been examined, typified and linked to currently recognized taxa in our recent works (Sokoloff & al. in Diversity 15: e176, e766, e785. 2023), to ensure the correct application of historical nomenclature and of nomenclatural priority. Acorus is represented by two species in North America: A. calamus L. (Sp. Pl.: 324. 1753) and A. americanus (Raf.) Raf. (New Fl. 1: 57. 1836) (based on A. calamus var. americanus Raf., Med. Fl. 1: 25. 1828) (Löve & Löve in Proc. Genet. Soc. Canada 2: 14. 1957; Wilson in J. Arnold Arbor. 41: 50. 1960; Packer & Ringius in Canad. J. Bot. 62: 2248–2252. 1984; Thompson, Syst. Araceae Acoraceae Temp. N. Amer. [Ph.D. Thesis, Univ. Illinois at Urbana-Champaign]. 1995; Thompson in Fl. N. Amer. Ed. Comm., Fl. N. Amer. N. Mexico 22: 124–127. 2000; Les, Aquatic Monocotyledons N. Amer.: 3. 2020). These two taxa are sometimes recognized as varieties (Wulff in Arch. Pharm. & Ber. Deutsch. Pharm. Ges. 287: 541. 1954; Röst in Pl. Med. (Stuttgart) 37: 289–307. 1979; https://powo.science.kew.org/, accessed 15 Aug 2023), i.e., A. calamus var. calamus and A. calamus var. americanus. The taxonomic status of A. calamus and A. americanus is confirmed in our forthcoming work (Sokoloff & al., submitted to Amer. J. Bot.), using extensive morphological and molecular phylogenetic evidence. Acorus americanus is a fertile diploid producing obtuse fruits with a few large seeds (see fig. 8A,B in Sokoloff & al. in Bot. J. Linn. Soc. 195: 189–215. 2021). Acorus calamus is a sterile triploid that propagates only vegetatively, producing acute parthenocarpic fruits with numerous small unfertilized ovules (see fig. 8C,D in Sokoloff & al., l.c. 2021). In North America, these species can be distinguished with certainty by leaf venation patterns: diploids have leaves with an indistinct midrib, whereas the midribs of triploid plants are prominently observable (Thompson, l.c. 1995; l.c. 2000). Rafinesque (l.c. 1828: 25–26) paid no attention to the fertility of the American plants but stated that Acorus calamus var. americanus has “oblong acute” fruits with “many minute slender seeds”. This indicates that he actually studied sterile triploid plants producing parthenocarpic fruits with numerous unfertilized ovules rather than seeds. Rafinesque did not provide a detailed description of the leaf characters of A. calamus var. americanus, but the illustration in its protologue shows leaves with an apparent midrib, which fits the idea that he studied triploid material. After 1825 and at the time of preparation of his Medical Flora, Rafinesque resided in Philadelphia, Pennsylvania (Call, Life Writings Rafinesque: 49. 1895), where he worked and collected plants as a private botanist. The original material of Acorus calamus var. americanus most likely originated from the vicinities of this town. According to Thompson (l.c. 1995), fertile diploids are very rare in Pennsylvania, and are known only from a few collections in the north. In contrast, sterile triploids are very common in Pennsylvania, and their distribution agrees with the diagnostic characters of triploids mentioned in the protologue. Rafinesque (Autik. Bot. 3: 196. 1840) indicated by the lack of a dagger at the species account that herbarium specimens of Acorus americanus were available for sale in a sufficient amount, thus evidencing that this taxon was easily accessible to him near the place of his residence, Philadelphia. It is not certain whether any of these specimens were prepared in direct connection with the protologue; anyway, no collections labelled as A. americanus by Rafinesque had ever been cited in taxonomic literature or were traced by the authors of this proposal. In the absence of any herbarium specimens, the only extant element of the original material of A. calamus var. americanus is the drawing provided of “Acorus Calamus” by Rafinesque (l.c. 1828: fig. 1). Thompson (l.c. 1995) selected this figure as the lectotype and designated an epitype of A. calamus var. americanus from Maine (Ogden & Steinmetz 2473 at CM), a collection widely distributed as part of Plantae Exsiccatae Grayanae, to accommodate the use of the name for diploid plants. As the characters indicated in the protologue, the original illustration, and the presumed original locality suggest that Rafinesque studied triploids, the current nomenclatural interpretation of Acorus calamus var. americanus as a diploid plant (Thompson, l.c. 1995) does not match the information in its protologue. The proposed epitype also does not match the lectotype it was intended to support. Furthermore, Thompson's designation of the lectotype and its supporting epitype cannot be considered effective because it was made in a Ph.D. thesis without an ISBN or ISSN or a printer's statement (ICN Art. 30.9 and Note 3, Turland & al. in Regnum Veg. 159. 2018). According to the intended lectotype, which is the only element of the original material in existence, the names Acorus calamus var. americanus and A. americanus should be placed in the synonymy of A. calamus. Among the remaining names published in Acorus, A. triqueter Turcz. ex Schott (Prodr. Syst. Aroid.: 578. 1860), described from Siberia, has priority for the purpose of naming diploid plants (Sokoloff & al., l.c. 2023: e766). Since its original publication, A. triqueter has never been accepted as a distinct species in North American or Russian floristic literature. The latter species name has never been applied to diploid plants; instead, it was misinterpreted as the earliest name for a tetraploid member of the A. calamus group (Löve & Löve, l.c.; Petersen in Nordic J. Bot. 9: 133. 1989; Bogner & Mayo in Kubitzki, Fam. Gen. Vasc. Pl. 4: 9. 1998). On the other hand, the use of Acorus americanus has been consistent among all North American botanists who accepted this name after its interpretation as a diploid plant by Löve & Löve (l.c.) in 1957. At present, the name A. americanus is accepted in numerous North American online databases, floristic, taxonomic and curatorial (e.g., https://plants.usda.gov/home/plantProfile?symbol=ACAM; https://kiki.huh.harvard.edu/databases/specimen_search.php?family=Araceae; http://northernontarioflora.ca/description.cfm?speciesid=1005163; https://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Acorus%20americanus; https://data.canadensys.net/vascan/name/Acorus%20americanus, all accessed 17 Aug 2023). Numerous non-taxonomic studies employed the use of the name A. americanus (e.g., in ethnopharmacology: Cybulska & al. in Sexually Transmitted Dis. 38: 667–671. 2011; ecophysiology: Calvo Polanco & al. in J. Environm. Qual. 43: 578–586. 2014; Equiza & Zwiazek in Botany 92: 541–550. 2014; reproductive biology: Smreciu & al. in Native Pl. J. 15: 219–221. 2014, 16: 19–22. 2015; conservation biology: Geiger & Banker in Ecol. Restorat. N. Amer. 30: 160–162. 2012). Acorus americanus has been used as the only representative of Acorales in several studies of molecular phylogenetics and evolution (e.g., Little & al. in Pl. Physiol. 177: 1124–1141. 2018; One Thousand Plant Transcriptomes Initiative in Nature 574: 679–685. 2019; Bélanger & al. in Pl. Physiol. (Lancaster) 192: 1183–1203. 2023). We believe that replacing the established name Acorus americanus with the long-obsolete and cytologically misinterpreted A. triqueter will create unnecessary complications in taxonomic literature and confusions among cytologists. In the interests of stability of plant nomenclature, we propose conservation of the basionym of A. americanus, A. calamus var. americanus, with a conserved type (Art. 14.1, final sentence), to fix its current application to the diploid species. We propose Ogden & Steinmetz 2473 (CM No. 313477 [barcode 0005], https://sernecportal.org/imglib/storage/portals/seinet/mam/CM/CM313/CM313477_1539789201_web.jpg), the ineffectively designated epitype of A. calamus var. americanus, as its conserved type, to retain the existing nomenclatural status quo. This collection fits the leaf and fruit characters considered diagnostic for the diploid species and has an advantage of being represented in many herbarium institutions worldwide. Thompson (l.c. 1995) studied the pollen stainability of CM No. 313477 and concluded that the pollen was fertile. The fertility is also clear from the occurrence of young fruits developing in the same inflorescence of CM No. 313477. The leaves have many equal-sized parallel vascular bundles (no midrib is present), which is the main morphological character that distinguishes American diploids from triploids (Thompson, l.c. 1995). The printed label of Ogden & Steinmetz 2473 (Plantae Exsiccatae Grayanae No. 1216) indicates that fruit material was collected in the same locality on 15 September 1942. The fruits are placed in envelopes mounted as part of CM No. 313477 and most other specimens of Plantae Exsiccatae Grayanae No. 1216 preserved in other herbaria. As type material should be collected at one time, these fruits are excluded from the type proposed for conservation but provide an additional evidence of plant morphology and fertility. DDS, https://orcid.org/0000-0001-6314-9767 ANS, https://orcid.org/0000-0001-6664-7657 The work of DDS is supported by the Ministry of Science and Higher Education of Russia (project 075-15-2021-1064). The work of ANS received no external funding.

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