808 Eucladium is a monotypic moss genus of Pottiaceae, which was established by Bruch & Schimper (in Bruch & al., 1846) for E. verticillatum, a species that in the early bryological literature was named Weissia verticilla- ta (e.g., Bridel, 1801, 1806; Schwägrichen, 1811), Grimmia verticillata (e.g., Turner, 1804; Smith, 1804; Weber & Mohr, 1807), and Coscinodon verticillatus (Bridel, 1826). This species has been known since the beginnings of bryology, and was described and illustrat- ed by Dillenius (1741) who gave the phrase-name Bryum pilosum verticillatum to the specimens collected by R. Richardson in York, England, and S. Brewer near Bangor, Wales, in Britain (Lindberg, 1883). In addition, he also cited, in synonymy, Ray’s (1724) Bryum tri- chodes brevifolium, angustis cauliculis, capitulis erectis parvis & minus aduncis, which seems to be the first recognition of this species. Dillenius’ phrase name was used in the binomial combination Bryum verticillatum by Linnaeus (1753) who cited the Dillenian page number and figure. For the subsequent half-century it remained a neglected and forgotten species, and it is missing from Hedwig’s (1801) Species Muscorum Frondosorum, the starting point for moss nomenclature (Sphagnum except- ed). In modern bryology there are serious differences of opinion regarding the post-1 January 1801 validation of “Bryum verticillatum”, and consequently the basionym of Eucladium verticillatum is variously cited. Following Index Muscorum (Wijk & al., 1962), currently consid- ered an authoritative source of nomenclatural informa- tion for mosses, it is generally accepted in most Floras, catalogues and checklists that the basionym of E. verti- cillatum is “Weissia verticillata (Hedw.) ex Brid.”, as if the name of the species were first validated in Weissia by Bridel (1801) on the basis of a pre-1801 publication by Hedwig. On the other hand, Podpra (1954) in his Conspectus Muscorum Europaeorum, which is still a real mine of information on early moss names, listed Grimmia verticillata Sm. as the basionym of this name, indicating that Smith (1804) was the first to provide a validly published name for the Linnaean “Bryum verti- cillatum”. We carefully checked the facts and found that neither of these names can be considered as the basionym of Eucladium verticillatum. Bridel (1801) provided only the name “Weissia ver- ticillata Hedw.”. The ascription of this name to Hedwig might have been interpreted as an indirect reference to a pre-1801 Hedwigian work in which this species might have been described or a reference to an earlier descrip- tion could be given. Hedwig published a good number of scientific works (Wissemann, 2000), four of which are fundamental treatments and are considered as the foun- dations of modern bryology. A careful search through all major bryological works of Hedwig (1782, 1784, 1787–1797) revealed that this species was completely uknown to him and that he never used the names Bryum verticillatum or Weissia verticillata. Thus, “W. verticilla- ta” in Bridel (1801) is a nomen nudum. The earliest publication of a name for the species in the post-1 January 1801 period was actually by Withering (1801) who validated Bryum verticillatum by providing a description and citing the Dillenian figure. If one goes back from the references that Bruch & al. (1846) mention under Eucladium verticillatum, via Ochyra & Zijlstra • The basionym of Eucladium verticillatum 54 (3) • August 2005: 808–810 The basionym of Eucladium verticillatum (Pottiaceae) Ryszard Ochyra 1 & Gea Zijlstra 2 1 Laboratory of Bryology, Institute of Botany, Polish Academy of Sciences, ul. Lubicz 46, 31-512 Kraków, Poland. r.ochyra@ib-pan.krakow.pl (author for correspondence) 2 Nationaal Herbarium Nederland, Utrecht University branch, Heidelberglaan 2, NL-3584 CS Utrecht, Netherlands. g.zijlstra@bio.uu.nl Evidence is provided that the first person to validly publish a name for the species that Linnaeus termed “Bryum verticillatum” in 1753 was Withering in 1801, and that his name actually constitutes the basionym of the well-known moss name, correctly cited as Eucladium verticillatum (With.) Bruch & Schimp. (Bryophyta, Pottiaceae). “Weissia verticillata (Hedw.) ex Brid.” of 1801, which has hitherto been considered the basionym of this binomial, is a nomen nudum; the combination Weissia verticillata was validly published by Bridel in 1806. Bryum verticillatum With. is lectotypified here with a specimen from Cumberland, England, that is pre- served at BM. KEYWORDS: Bryophyta, Dillenius, Eucladium, Hedwig, Linnaean name, nomenclature, Pottiaceae, typifica- tion.