In taxonomy, the term incertae sedis (abbreviated inc. sed.) is used for a taxon when its broader relationship to other taxa is unknown. The first person who used the term in botany was probably Antoine-Laurent de Jussieu. In his book Genera Plantarum of 1789 he listed a few plantae incertae sedis.
Reasons why a taxon might be classified as incertae sedis include:
- The description is not detailed enough to permit a clear classification.
- A scientific publication about a taxon does not focus on its classification. The taxon is labeled incertae sedis, because the authors of the publication do not want to guess where the taxon belongs.
- Different researchers may have different opinions of where a taxon should be classed. Until the conflicts are resolved, the taxon is classed as incertae sedis.