Sui generis
A similar case that led to the use of the label "sui generis" is the relationship of New Caledonia relative to France, because the legal status of New Caledonia can aptly be said to lie somewhere between a French overseas collectivity and a sovereign nation. Although other examples of such status for other dependent or disputed territories may exist, this arrangement is unique within the French realm.
Senecio eboracensis
The science of this plant is that it is a hybrid species whose parents are the self-incompatible and promiscuous Sicilian "Senecio squalidus" (also known as Oxford ragwort) and the self-compatible and tenacious "Senecio vulgaris" (also known as Common groundsel). Like "S. vulgaris", "S. eboracensis" is self-compatible, however, it shows little or no natural crossing with its parent species, and is therefore reproductively isolated, indicating that strong breed barriers exist between this new hybrid and its parents.
It is thought to have resulted from a backcrossing of the F1 hybrid of its parents to "S. vulgaris". "S. vulgaris" is native to Britain, while "S. squalidus" was introduced from Sicily in the early 18th century; therefore, "S. eboracensis" has speciated from those two species within the last 300 years.