A survey of the descriptions of novel bacterial species published in the period 1996–2006 revealed that a large number of taxonomic descriptions are still based on one or a few strains. This situation determines that not only species descriptions, but also proposals to create higher ranks, are actually based on very few strains, which could produce a highly biased scenario. The encouragement to include a reasonable number of strains in species descriptions has been largely disregarded after its proposal, since acceptance of such descriptions relies mainly on editors’ and reviewers’ opinions. This observation and other considerations lead us to propose the creation of the status species proponenda (sp. pr.), as a compromise between the need for scientific description of biodiversity and exchange of data and the good taxonomic practice of including a sufficient number of strains in descriptions of species and higher taxonomic ranks. Christensen et al. (2001) presented a detailed report on the trend of describing novel taxonomic units (species, genera and families) based on a very small number of isolates or even one isolate. This is not considered good taxonomic practice, since descriptions based on single isolates might not be reliable and good theoretical reasons to include many isolates in taxonomic studies have been documented (Sneath, 1976; Tru¨per & Schleifer, 1992). With this premise, Christensen et al. (2001) suggested that Recommendation 30b of the International Code of Nomenclature of Bacteria (the Bacteriological Code; Lapage et al., 1992) be modified as follows: ‘Descriptions should be based on as many strains as possible (minimum five), representing different sources with respect to geography and ecology in order to be well characterized both phenotypically and genotypically, to establish the centre (from which the type strain could be chosen) and the extent of the cluster to be named. In addition, comparative studies should be performed, including reference strains that represent neighbouring species and/or genera, in order to give descriptions that are sufficiently detailed to allow differentiation from these neighbours’. On this basis, the ad hoc committee for the re-evaluation of the species definition in bacteriology encouraged microbiologists to base a species description on more than a single strain (Stackebrandt et al., 2002). We performed a review of the descriptions of novel species and genera published between 1996 and 2006. Lists of names published each year were obtained from J. P. Euze´by’s List of Prokaryotic names with Standing in Nomenclature, in particular from http://www.bacterio. cict.fr/allnamesac.html for names validly published in 1996 and 1997 and from specific yearly lists for the years 1998–2006 (1998, http://www.bacterio.cict.fr/twothousand/ ninetyeight.html; 1999, http://www.bacterio.cict.fr/twothousand/ ninetynine.html; 2000, http://www.bacterio.cict.fr/twothousand/ changestwothousand.html; 2001, http://www.bacterio.cict. fr/twothousand/twothousandone.html; 2002, http://www. bacterio.cict.fr/twothousand/twothousandtwo.html; 2003, http://www.bacterio.cict.fr/twothousand/twothousandthree. html; 2004, http://www.bacterio.cict.fr/twothousand/ twothousandandfour.html; 2005, http://www.bacterio. cict.fr/twothousand/twothousandfive.html; 2006, http:// www.bacterio.cict.fr/twothousand/twothousandsix.html). Descriptions of new combinations, new subspecies and Candidatus were omitted, as well as descriptions of novel higher taxonomic ranks that did not contain novel species. The results of the analysis are reported in Fig. 1; species numbers are plotted for each year according to the number of strains which was included in the original description. It is evident that, after the ‘encouragement’ of 2002, the trend of taxonomic descriptions has not changed, with even an increase in the incidence of proposals of novel species based on one or a few strains. It could therefore be concluded that the suggestion of the ad hoc committee (Stackebrandt et al., 2002) was not properly followed by the scientific community. In the publication procedure, the encouragement becomes the responsibility of single editors and reviewers, and in practice it is extremely difficult to rule that a description based on a single strain or very few strains should be rejected simply because of the small number of strains included, if the taxonomic characterization is well International Journal of Systematic and Evolutionary Microbiology (2007), 57, 2185–2187 DOI 10.1099/ijs.0.64931-0 64931 G