Incertae sedis, latin for of uncertain placement, or problematica are terms used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as enigmatic taxa. In the system of open nomenclature, uncertainty at specific taxonomic levels is indicated by incertae familiae (of uncertain family), incerti subordinis (of uncertain suborder), incerti ordinis (of uncertain order) and similar terms.
It was showed in 2007 that Oxygastra curtisii does not belong in the family Corduliidae. It constitutes probably the phylogenetically most isolated species in Europe and is probably its oldes relict. It is not clear in which family it should be placed and is therefore considered incertae sedis.