(2972) Proposal to conserve the name <i>Aster annuus</i> (<i>Erigeron annuus</i>, <i>Phalacroloma annuum</i>) (<i>Asteraceae</i> / <i>Compositae</i>) with a conserved type

(2972) Aster annuus L., Sp. Pl.: 875. 1 Mai 1753 [Angiosp.: Comp.], nom. cons. prop. Typus: Finland, Ab. Parainen, Paraisten kirkko, kirkon etelä-sivustan ulkopuolisella puistonurmikolla ja kirkkoaidan kupeella villiintyneenä [on park lawn and by fence at the southern side of the church, semi-natural], 4 Aug 1984, Silkkilä (H barcode H703598), typ. cons. prop. Aster annuus L. was described by Linnaeus (Sp. Pl.: 875–876. 1753) with the note “Habitat in Canada”, but its lectotype (BM000647093, ex Herb. Clifford) designated by Scott (in Bosser & al., Fl. Mascar. 109: 106. 1993) is most probably a plant cultivated in Europe (see Sennikov & Kurtto in Memoranda Soc. Fauna Fl. Fenn. 95: 40–59. 2019). Nowadays that species is most commonly recognized as Erigeron annuus (L.) Desf. (Tabl. École Bot.: 102. 1804), or sometimes as Phalacroloma annuum (L.) Dumort. (Fl. Belg.: 67. 1827). Three entities were usually recognized within this polymorphic species (or species aggregate); they were treated as subspecies E. annuus subsp. annuus, E. annuus subsp. septentrionalis (Fernald & Wiegand) Wagenitz (≡ E. ramosus var. septentrionalis Fernald & Wiegand in Rhodora 15: 60. 1913), and E. annuus subsp. strigosus (Muhl. ex Willd.) Wagenitz (≡ E. strigosus Muhl. ex Willd., Sp. Pl. 3: 1956. 1803) (see Wagenitz in Hegi, Ill. Fl. Mitt.-Eur., ed. 2, 6/3(2): 96. 1965); or sometimes accepted as “narrow” species in the segregate genus Phalacroloma Cass. (e.g., Tzvelev in Novosti Sist. Vyssh. Rast. 28: 148. 1991, in Fl. Evropeiskoi Chasti SSSR 7: 203–204. 1994, etc.): P. annuum (L.) Dumort. s.str., P. septentrionale (Fernald & Wiegand) Tzvelev, and P. strigosum (Muhl. ex Willd.) Tzvelev (see a taxonomic overview and nomenclatural citations in Sennikov & Kurtto, l.c.). At present, several related taxa of the Erigeron annuus group native to North America, usually recognized as three subspecies or segregate species, are widespread agricultural and/or environmental weeds and dangerous invasive plants widely naturalized in Europe and several regions of Asia and occurring as casual aliens in many other parts of the world (e.g., Patamsytė & al. in Centr. Eur. J. Biol. 8: 898–911. 2013; Otto & Verloove in Willdenowia 49: 427–430. 2019; Axmanová & al. in J. Veg. Sci. 32: e12994. 2021; Dubyna & al. in Diversity 14: art. 1085. 2022, https://doi.org/10.3390/d14121085; Liu & al. in Frontiers Pl. Sci. (Online journal) 13: 994367. 2023, https://doi.org/10.3389/fpls.2022.994367, and references therein; see also an overview in Sennikov & Kurtto, l.c.). Frey & al. (in Bot. Helv. 113: 1–14. 2003) provided evidence that E. annuus s.l. (including the taxon earlier commonly treated as subsp. or var. septentrionalis) is represented by agamospermous triploids (see also Edwards & al. in Int. J. Pl. Sci. 167: 93–101. 2006), while plants corresponding to E. strigosus s.str. are (mostly?) sexual di- or tetraploids. Various taxa (recognized as species or infraspecific entities) of that group seem to differ by their invasive potential and ecological/phytosociological peculiarities in various geographical and geoclimatic regions of the world. Because of that, precise identification and stability of nomenclature of these taxa are important. The lectotype of Aster annuus designated by Scott (l.c.) is a fragment representing the uppermost part of a plant, with just a few upper cauline leaves under the synflorescence (BM000647093; https://plants.jstor.org/stable/10.5555/al.ap.specimen.bm000647093, all online sources here and below initially accessed 24 Mar 2022 and re-checked 24 May 2023). As Sennikov & Kurtto (l.c.: 44) noted, the “whole fragment seems to be covered with a short appressed pubescence, except for the involucres which are covered with long hairs. The colour of ray flowers is no longer recognizable” [emphasis added – S.M.]. It seems, however, that Sennikov & Kurtto (l.c.) were not completely sure about the precise taxonomic identity of the type and because of that they used indirect evidence, such as information from historical records, for example, about the white color of ray flowers of the “typical” A. annuus as opposed to the lilac color in another infraspecific entity. However, they also admitted that at least some historical records report the color of ray flowers as “white, possibly with a slight ‘red’ tint”. Sennikov & Kurtto (l.c.: 45) also mentioned the present-day prevalence of the so-called “septentrionalis” morphotype in the Netherlands, including the area where Clifford's garden was originally located. However, that additional argument cannot be considered convincing because the present distribution patterns do not necessarily reflect the distribution of particular morphotypes in the mid-18th century. Despite the remaining doubts regarding the precise identity of the lectotype of Aster annuus, Sennikov & Kurtto (l.c.: 45) concluded that “The morphology of the type specimen of E. annuus and the early descriptions and illustrations of this species indicate that the plants described by Linnaeus (1753) belong to the segregate currently known under the epithet ‘septentrionalis’ […]”, and because of that they synonymized Erigeron annuus subsp. septentrionalis under E. annuus subsp. annuus (E. annuus s.str.) and described the entity previously commonly known as E. annuus subsp. annuus as a new subspecies, E. annuus subsp. lilacinus Sennikov & Kurtto (l.c.: 47), with a type from Finland (H703598, see above). Sennikov & Kurtto (l.c.: 54) explained that they preferred the option of coining a new name and new taxon, “strictly following the rules of botanical nomenclature, over the possibility to conserve the name E. annuus [in fact, Aster annuus – S.M.] with a new type, since only by conservation the application of this name may be retained in the sense established by Wagenitz (1965)”. The new species-rank combination E. lilacinus (Sennikov & Kurtto) Sennikov (in Sennikov & al. in Wulfenia 27: 2. 2020) was published soon thereafter; the author reported that taxon for Taiwan and Vietnam but did not mention that the species name is directly applicable to plants previously almost universally known under the name E. annuus s.str. Thus, because of the new interpretation of the possible taxonomic identity of the standing type of Erigeron annuus by Sennikov & Kurtto (l.c.) we have the situation that the widespread taxon formerly generally known as E. annuus s.str. should be now called E. lilacinus or E. annuus subsp. lilacinus, while the taxon earlier usually recognized under the name E. annuus subsp. septentrionalis (or under other names based on the basionym E. ramosus var. septentrionalis, see above) should be now recognized as E. annuus subsp. annuus or E. annuus s.str. These name shifts are confusing for agriculturalists (for whom taxa of the E. annuus aggregate are important as weeds), conservationists (who, inter alia, are dealing with large-scale invasions of taxa of the E. annuus group), managers of biodiversity databases (see examples below), and other end users of taxonomic information. The re-interpreted taxonomic identity of Erigeron annuus s.str. and the introduction of a new subspecies name (E. annuus subsp. lilacinus) and a species-rank combination (E. lilacinus) have already caused considerable confusion in online biodiversity databases. For example, the following taxa of the E. annuus group (only those occurring as introduced and/naturalized in Eurasia and elsewhere) are currently recognized in the Plants of the World Online (POWO) database: (1) Erigeron annuus subsp. annuus (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77231050-1): reported as native and widespread in North America, widely introduced in Europe and known in several regions of Asia; (2) E. annuus subsp. lilacinus (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77196962-1): reported globally only as introduced (!) and only for “Baltic States, Finland, Sweden, Taiwan, Vietnam”; the East Asian records are apparently based on data from Sennikov & al. (l.c., 2020); (3) E. strigosus var. strigosus (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77231831-1): reported as native in North America and introduced in Germany in Europe and in several countries and regions of Asia, and (4) E. strigosus var. septentrionalis (despite the proposed synonymization of that name with E. annuus s.str. by Sennikov & Kurtto, l.c.; https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:94165-2): reported as native in North America and introduced in most of Europe, the Caucasus, and the Russian Far East. In the Global Biodiversity Information Facility (GBIF) online database Erigeron annuus subsp. lilacinus (https://www.gbif.org/uk/species/3117449) is treated as a synonym of E. annuus (sensu lato?); however, records identified as E. annuus subsp. lilacinus (https://www.gbif.org/uk/species/10912845) are also separately reported from Finland, Sweden, the Baltic states, and Italy. Much effort will be needed now to sort out those confusing records. Moreover, considering the huge variability of the Erigeron annuus aggregate and the large number of names published in North America and Europe for taxa of that group, it is quite possible (or almost certain?) that some earlier species-rank or infraspecific name(s) will be found (e.g., among several not yet typified names) for the taxon newly described as E. annuus subsp. lilacinus (E. lilacinus). That may bring further taxonomic instability and unnecessary nomenclatural changes. The names Erigeron lilacinus or E. annuus subsp. lilacinus have been unquestionably accepted in only a limited number of publications (e.g., Sennikov & Kurtto, l.c.; Sennikov & al., l.c.; Sennikov & Lazkov in Biodivers. Data J. 9: e75590 [pdf pp. 17–20]. 2021, https://doi.org/10.3897/BDJ.9.e75590; Sennikov & Galasso in Ital. Bot. 11: 108. 2021; Aymerich in Butl. Inst. Catalana Hist. Nat. 86: 121–122. 2022), and in some of those publications the identity of these names with plants previously called E. annuus s.str. was not mentioned. Thus, the proposed synonymization of the names E. lilacinus and E. annuus subsp. lilacinus under E. annuus s.str. (by conservation with a conserved type) will not disrupt the common usage and application of accepted names in that group. In my opinion, the best action for preventing further nomenclatural and taxonomic confusion would be to maintain the traditional taxonomic usage of the name Aster annuus (now usually accepted as Erigeron annuus) and all nomenclatural combinations based on it, which could be best achieved by conservation of the mentioned Linnaean name with a conserved type taxonomically and nomenclaturally corresponding to the designated holotype of E. annuus subsp. lilacinus. The proposed conservation will ensure the well-established usage (see Wagenitz, l.c., etc.) of the widely accepted names for infraspecific taxa of E. annuus. SLM, https://orcid.org/0000-0002-3570-3190 I am grateful to John McNeill (Royal Botanic Garden, Edinburgh, Scotland, U.K. & Royal Ontario Museum, Toronto, Ontario, Canada) for his valuable advice on nomenclature and to John H. Wiersema (Smithsonian Institution, Washington, D.C., U.S.A.) for his useful comments and editing.

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