(1633) Proposal to conserve the name Pinnularia gastrum with a conserved type (Bacillariophyta)

Abstract

Ehrenberg's (Verbr. Mikrosk. Lebens Amerika: 133, t. III, [group] VII, f. 22. May-June 1843; reprinted in Abh. K'nigl. Akad. Wiss. Berlin 1841: 421, t. III, [group] VII, f. 22. Sep.-Nov. 1843) description and illustration of this species were based on specimens in marine material from Vera Cruz, Mexico, but he also recorded it in freshwater material from Newhaven, Conn., U.S.A., and from Iceland (l.c. May-June 1843: 288). Kiitzing (Kieselschal. Bacill.: 94, t. 28 f. 56. 1844) transferred the species to Navicula without seeing a specimen, his figure being a copy of Ehrenberg's. Ehrenberg later (Mikrogeologie: t. V, [group] I, f. 12. 1854) provided a figure of R gastrum from Iceland and another (Mikrogeologie, t. XV f. 23. 1854) of a specimen from Down, Mourne Mountains, Ireland. Ehrenberg's original figure, of a marine specimen from Vera Cruz, Mexico, shows a valve c. 40 ?tm x 20 gm with slightly protracted apices and parallel striae, but his later figures, from freshwater material, whilst similar in outline, show radiate striae; they clearly represent a different species from that shown in his original figure. Donkin (Nat. Hist. Brit. Diat.: 22, pl. III f. 10. 1873) described and figured as Navicula gastrum a diatom from Loch Mourne (sic), saying that it came from the same deposit as that examined by Ehrenberg. His illustration shows a diatom with more broadly rounded apices than those illustrated by Ehrenberg and Ktitzing, with radiating striae and with some shortened striae intercalated opposite the central nodule. Cleve & Grunow (in Kongl. Svenska Vetenskapsakad. Handl. n.s. 17(2): 31. 1880) explicitly followed Donkin's concept of the species, questioning whether he illustrated the same taxon as Ehrenberg. Since then the name Navicula gastrum (Ehrenb.) Ktitz. has been applied in Donkin's sense in all the works used for diatom identification (Van Heurck, Syn. Diatom. Belg., Atlas: pl. VIII f. 25. 1880; Cleve in Kongl. Svenska Vetenskapsakad. Handl. n.s. 27 (3): 22. 1896 [for this date see Ross in Brit. Mus. (Nat. Hist.) Botany 3: 51. 1963]; Van Heurck, Treatise Diatom: 186, pl. 3. f. 134. 1896; Traits Diatom.: 186, pl. 3 f. 134. 1899; Hustedt in Pascher, Siisswasserflora, ed. 2, 10: 305, f. 537. 1930; in Rabenhorst, Krypt.-Fl. 7 (3): 799, f. 1771. 1966; Proshkina-Lavrenko & al. Diatom. Analis, 3: 187, t. 60 f. 6. 1950; Zabelina, Kiselev, ProshkinaLavrenko & Sheshukova, Diatom. Vodorosli: 324, f. 187, 1. 1951, Patrick & Reimer, Diatoms United States, 1: 518, pl. 49, f. 14. 1966; Krammer & Lange-Bertalot in Ettl, Gerloff, Heynig & Mollenhauser (eds.) Siisswasserflora 2, Bacillariophyceae. 1 Teil, Naviculaceae: 143, f. 49, 4-6. 1986) until the most recent (Cox, Identific. Freshwater Diatoms from Live Material, 87, f. 28a. 1996; Hartley, Atlas Brit. Diatoms: 142. 1996) in which Placoneis gastrum (Ehrenb.) Mereschk. is used in the same sense. Mereschkowsky (Beih. bot. Centralbl. 15: 1-30. 1903) separated the genus Placoneis from Navicula Bory and included within it several species, one of which was Placoneis gastrum (Ehrenb.) Mereschk., based on Pinnularia gastrum Ehrenb. He did not, however, designate any type of the generic name. Until recently other authors did not accept the separation of Placoneis from Navicula. Cox (in Diatom Research 2: 145-157. 1987), however, drew attention to the differences that separated the two genera and, at the same time, designated Placoneis gastrum (Ehrenb.) Mereschk. as the type of the genus, applying the name in Donkin's sense. The separation of Placoneis Mereschk. from Navicula Bory has been accepted in the most recent publications. Since the name Navicula gastrum has been consistently used in Donkin's sense for almost a century and a half, it would clearly cause confusion to use for the species a name with any other epithet. No specimens representing original material ofPinnularia gastrum survive in Ehrenberg's collection at BHU (Cox in Bot. J. Linn. Soc. 141: 57. 2003), but a neotype that would accord with established practice would be in serious conflict