One of possibly many scientific names belonging to a taxon. Two types of synonyms are considered here. Homotypic synonyms are based on the exact same type specimen, or holotype. Homotypic synonyms are declared through a 'nomenclatural act', that is, published in the scientific literature following the formal rules of the International Code of Nomenclature for algae, fungi, and plants (ICN). For example, Achnanthes minutissima was transferred to the genus Achnanthidium and renamed Achnanthidium minutissimum. These two names are homotypic, nomenclatural, or objective, synonyms.

Heterotypic synonyms are based on different type specimens. These synonyms rely on the opinions of taxonomists rather than on the formal, nomenclatural rules. For example, Gomphonema louisiananum was first described by Kalinsky (1984). Later, this same diatom was described as Gomphonema patrickii by Kociolek and Stoermer (1995), using a different type specimen. These two names are heterotypic, or subjective, synonyms.

This web flora emphasizes objective synonyms. Expert contributors and reviewers determine the relevant objective synonyms to include on each species page and list them under the heading, SYNONYMS. We consider the relevant synonyms to be those that analysts might typically encounter. We also include names that we consider to be subjective synonyms under the heading, REPORTED AS. This heading also includes errors in identification published in various floras.

Image Credit: ICN
Definition of homotypic synonym from the International Code of Nomenclature for algae, fungi, and plants (ICN). For more information, see
Achnanthidium Minut
Image Credit: Marina Potapova
Light micrograph of raphe valve of Achnanthidium minutissimum. Scale bar = 10 µm. A homotypic synonym for this diatom is Achnanthes minutissima.
Gomphonema Patricki1 53X233
Image Credit: Loren Bahls
Light micrograph of Gomphonema louisiananum. Scale bar = 10 µm. A heterotypic synonym for this diatom is Gomphonema patrickii.