5.1. The relative order of the ranks specified in Art. 3 and 4 must not be altered (see Art. 33.9 and 33.12).
5A.1. For purposes of standardization, the following abbreviations are recommended: cl. (class), ord. (order), fam. (family), tr. (tribe), gen. (genus), sect. (section), ser. (series), sp. (species), var. (variety), f. (forma). The abbreviations for additional ranks created by the addition of the prefix sub-, or for nothotaxa with the prefix notho-, should be formed by adding the prefixes, e.g. subsp. (subspecies), nothosp. (nothospecies), but subg. (subgenus).
(c) 2006, by International Association for Plant Taxonomy. This page last updated 10.03.2007 .