Auctorum indicates that a name inbotany andzoology is used in the sense of subsequent authors, and not in the sense as established by the original author. Itsetymology derives from the Latin word forof authors, and is abbreviatedauct. orauctt.
Some species names have been used twice for different species so the author of the name needs to be identified. For example "Leucospermum bolusii auct. Gandoger" for the species that was named as such by Gandoger. It is often used in conjunction withnec ornon to indicate a misapplied name, e.g. "Leucospermum bolusii auct. non Gandoger" would mean the species not named by Gandoger.
It may be qualified to indicate the number of authors, e.g.auctorum multorum (abbreviatedauct. mult.), Latin forof many authors, indicating that many subsequent authors used a name in a different sense to the original author, and also bynon to giveauctorum non (auct. non), to indicate that a following author is not the author of the species.
Leucospermum bolusii is a name that was used twice for different species. The first time was byMichel Gandoger in 1901. Since this name wasvalidly published, used for a species that did not already have a name and the name had not already been used for another species, it is thecorrect name.[1] The list ofsynonyms ofLeucospermum cordifolium includesLeucospermum bolusii described byEdwin Percy Phillips in 1910. This name however was already taken. So,Leucospermum bolusiiE.Phillips, 1910 is a laterhomonym ofLeucospermum bolusiiGandoger, 1901.[1] If the nameLeucospermum bolusii is used in a later publication, the botanical author needs to make clear which one is meant, and which one isn’t. Hence, the species of 1901 would beLeucospermum bolusii auct. Gandoger, while the synonym ofLeucospermum cordifolium, isLeucospermum bolusii E.Phillips, 1910auct. non Gandoger.
TheFlora Europaea gives one of the synonyms ofCistus clusii as "C. libanotisauct. mult., non L.",[2] meaning that many authors misapplied the nameCistus libanotis to the speciesCistus clusii thereby using this name differently from the original author,Carl Linnaeus.