Basionym is a term used in botany

Botany

Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...

, regulated by the International Code of Botanical Nomenclature. It applies, for instance, when the binomial name of a species is changed (for taxonomic

Taxonomy

Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 or nomenclatural reasons) and the new name is based on an earlier name, the basionym.

The basionym of the name Picea abies (the Norway Spruce), for example, is Pinus abies. The species was originally named Pinus abies by Carolus Linnaeus

Carolus Linnaeus

Carl Linnaeus , also known after his ennoblement as , was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of the fathers of modern ecology...

; later botanist Karsten

Gustav Karl Wilhelm Hermann Karsten

Gustav Karl Wilhelm Hermann Karsten was a German botanist and geologist. Born in Stralsund, he followed the example of Alexander von Humboldt and traveled 1844-56 to the north of South America. He died 1908 in Berlin-Grunewald....

 decided it should not be in the same genus Pinus as the pine

Pine

Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...

s, but in a separate genus: he transferred it to the genus Picea (the spruces).

The term basionym is defined by the International Code of Botanical Nomenclature:

"basionym. A previously published legitimate name-bringing or epithet-bringing synonym from which a new name is formed for a taxon of different rank or position (Art. 33.4, 49.1 and 52.3)"