Baronia

Baronia brevicornis, commonly known as the short-horned baronia, is a species of butterfly in the monotypic genus Baronia and is placed in a subfamily of its own, the Baroniinae, a sister group of the remainder of the swallowtail butterflies. It is endemic to a very small area of Mexico, where the distribution is patchy and restricted.
The genus is named after a Mr Baron who collected the first specimen in the Sierra Madre region of Mexico. The species was then described by Salvin.
Morphological characteristics include an abdominal scent organ in females.
"Baronia" is unique among swallowtail butterflies or their relatives in having an "Acacia" species, "Acacia cochliacanha" (family Leguminosae) as its larval food plant.
Taxonomy.
"Baronia brevicornis" is of particular importance due to its relict nature and uncertain relationship to other subfamilies such as the Parnassiinae. It is now considered to represent the monotypic subfamily Baroniinae. The butterfly was considered as the most primitive extant papilionid taxon and shares some features with the fossil taxon Praepapilio, however a comprehensive 2018 molecular phylogeny suggests that they are a sister group of the remainder of the Papilionidae.
References.
Illustrated works: