These definitions of nomenclatural terminology were prepared with the assistance of Dr. Werner Greuter (Chairman, Editorial Committee for the ICBN). They offer only a general, and much-simplified, explanation of the categories of unaccepted names. As such, they are intended for GrainTax users who are unfamiliar with Greuter International Code of Botanical Nomenclature [ICBN]. Those users interested in more details about nomenclatural rules and their legalistic complexities should consult the ICBN or its web-based version http://www.bgbm.fu-berlin.de/iapt/nomenclature/code.
Illegitimate names are rejected under ICBN Articles 52 and 53. A name is illegitimate when (a) it was proposed as a replacement for an earlier name that should have been adopted or whose epithet should have been adopted (superfluous names) or (b) the same name had been published earlier for a different taxon (later homonyms).
Names not validly published are those that did not fulfil all relevant conditions deemed to apply under the ICBN (Art. 32-45) at the time when they were published. Basic requirements for valid publication, applicable irrespective of date, include definite acceptance of the name by its author and provision of a description of the taxon (or at least a reference to a description published earlier). Further conditions have been added, including use of Latin in the description of new taxa, statement of a type, or, for new combinations, full and direct citation of the so-called basionym (name of the epithet used in the new combination).
Ambiguous names are those that are rejected (ICBN, Art. 57), because they have been widely and persistently used in the wrong sense (i.e., for a taxon that does not include their nomenclatural type) so that using them correctly would now cause confusion. In the case of Ae. ovata L., this situation has occurred because the Linnaean original material includes elements of two different UM-genome species. The different handling of this initial ambiguity by various botanists has caused the confusion and eventual rejection of the name. Ambiguous names also may be formally rejected under Art. 56.
Synonymous names. More than one legitimate name often exists for the same taxon. Under the ICBN (Art. 11), only one of these is accepted, normally the earliest one in the appropriate rank, or the appropriate combination based on it; the other becomes a (Legitimate) Synonym. In some cases, the same taxon can have different accepted names when placed in different genera (or species) concepts, e.g., Ae. geniculata versus T. vagans , or at different ranks.