In taxonomy, the person who published the first valid name of a taxon. The name of the author, or a recognized abbreviation of it, should follow the name of the taxon for it to be complete. Many plant taxa are followed by L. (for Linnaeus). If the rank of a taxon at the genus level or below is changed but the name or epithet retained then the name of the original author is also retained in brackets before the name of the person who made the change. For example, Medicago polymorpha var. orbicularis L. was raised to the species level by Allioni and is thus named Medicago orbicularis (L.) All. A similar procedure is followed if a taxon at the subgeneric level is transferred to another taxon but retains its epithet.
If a name proposed by one person but not published by him is published by another and ascribed to the first author then the taxon is followed by the name of the first author followed by ex (described by) and then the name of the publishing author. For example, the Corsican speedwell is Veronica repens Clarion ex DC. (DC. for De Candolle). The citation of authors in this way helps other workers find the original descriptions and type specimens.