(2721) Proposal to conserve the name Chara flexilis (Nitella flexilis) (Characeae) with a conserved type

Abstract

(2721) Chara flexilis L., Sp. Pl.: 1157. 1 Mai 1753, nom. cons. prop. Typus: [United Kingdom, England], E. Sussex, Catsfield [nr. Battle]. “5 95” [Mai 1895]. Salmon (BM barcode BM013735408), typ. cons. prop. The name Nitella flexilis is used widely for a cosmopolitan taxon known from Europe, Asia, Africa, South America, and North America. It is recognized to be a monoecious species with branchlets without or with only one furcation, no cortication and single-celled terminal branchlet segments (dactyls) (Migula, Charac. Deutschl.: 132. 1890; Allen, Charac. America 2: 6. 1893; Gollerbach & Krasavina, Opredel. Presnovodn. Vodorosli SSSR 14: 55. 1983; Krause in Ettl & al., Süßwasserfl. Eur. 18: 146. 1997; Ling & al. in Nova Hedwigia 71: 69–94. 2001; Muller & al. in Cryptog. Algol. 38: 201–251. 2017; Blindow & al. in Nova Hedwigia 107: 49–90. 2018). Nitella opaca is a related species, but differentiated by dioecy. In some treatments, N. opaca was included in N. flexilis (e.g., Wood in Wood & Imahori, Monogr. Charac.: 372–391. 1965; Moore, BSBI Handb. 5: 88. 1986) because of the vegetative similarity of the two species. Linnaeus (Sp. Pl.: 1157. 1753) provided a very broad diagnosis “CHARA caulium articulis inermibus diaphanis superne latioribus” (Chara with unarmoured [without cortication], diaphanous stems and branchlets, broader in upper part), and adopted a treatment of the genus closely based on that in his Flora Suecica (Linnaeus, Fl. Suec.: 362–363. 1745). His concept of Chara flexilis could be used for almost all the ecorticate Characeae known at that time, and which today includes members of five genera, i.e., Chara, Lamprothamnium, Nitella, Nitellopsis and Tolypella. Agardh (Syst. Alg.: 124. 1824) included the species in his new genus Nitella and refined its description to read “N. flexilis, caule trichotomo pelucido, ramulis furcatis, nuculis alaribus solitariis” (stems thread-like, transparent, with forked branchlets, and oosporangia solitary and auxiliary (to one side). He included Linnaeus's C. flexilis as a synonym of N. flexilis and of no other taxon, but added “[quoad partem]”, presumably because of his inclusion under N. nidifica C. Agardh of Linnaeus's first recognition of the species in “Linn. it. Gothl. p. 215” (Linnaeus, Öländ. Gothl. Resa: 215. 1745). Agardh's generic description (Agardh, l.c.: xxvii) was later clarified by Leonhardi (in Verh. Naturf. Vereins Brünn 2: 155–158. 1864) and Braun (Consp. Charac. Europ.: 1–3. 1867) to include characters of the reproductive structures and branchlets. The material in the Linnaean herbarium (Herb. Linnaeus No. 1088.5, LINN) that was under the name Chara flexilis L. has a question mark following “flexilis” – obviously added later – and does not bear the Species plantarum number; it also disagrees with Linnaeus's diagnosis. It is probably a later addition to the herbarium and is certainly not original material. Furthermore, it is not even a Nitella but according to our identification a male Chara connivens, a corticated species of Chara. In the absence of a specimen in the Linnaean herbarium, another source must be sought for a type specimen to determine the application of the name. Wood (in Trans. Amer. Microscop. Soc. 79: 224. 1960) attempted to solve this problem by selecting as type one of the specimens of Nitella upon which Ray (Syn. Meth. Stirp. Brit., ed. 3: 133. 1724) based his “Chara translucens minor flexilis”, a synonym cited by Linnaeus (1753). The specimen details are: England. Suffolk, Henly, near Ipswich, Buddle in Herb. Sloane 117: 10 (BM-SL). However, Linnaeus did not examine the plants in Sloane's herbarium (Jarvis, Order out of Chaos. 2007) and, although Wood called the specimen the “LECTOTYPE”, it is not original material, and so Wood's action is an effective neotypification (Art. 9.10 of the ICN; Turland & al. in Regnum Veg. 159. 2018). We examined this specimen and found that it is a female dioecious plant which would be assigned to Nitella opaca according to the usage and species concepts of today. Application of the name N. flexilis to the species currently known as N. opaca would not favour the goal of nomenclatural stability enunciated in the Shenzhen Code (Turland & al., l.c.). We therefore formally propose to conserve Nitella flexilis with a new type (Art. 14.9). If Wood's neotypification were to stand, it would mean that the name N. flexilis should be applied to the taxon currently known as N. opaca. Meanwhile, the taxon widely understood as N. flexilis would need to be renamed. The next legitimate name applicable to the species may be Nitella spanioclema J. Groves & Bull.-Webst. (in J. Bot. 57: 1. 1919), if this is actually the same species as N. flexilis (a thorough genetic and morphological analysis has not yet been undertaken). In the absence of any original material, we propose as a conserved type a more recent collection from the material currently lodged in the Natural History Museum, London (BM). This gathering demonstrates the most characteristic features of the species to which the name N. flexilis is currently applied. TG, https://orcid.org/0000-0001-7692-8348 MTC, https://orcid.org/0000-0003-0516-7275