Butterfly gladiolus or goldblotch gladiolus is one of the approximately one hundred and sixty species of gladiolus endemic to South Africa. Unlike the genus Watsonia (featured on BPotD a couple days ago), the genus Gladiolus extends beyond the borders of South Africa; it can be found throughout much of sub-Saharan Africa and parts of Eurasia, though its centre of diversity remains in South Africa.
Within the globally widespread family Iridaceae, Gladiolus belongs to the Old World subfamily Crocoideae, along with Watsonia, Crocosmia, Dierama, Crocus and Babiana. Iridaceous plants not belonging to the Crocoideae featured on BPotD to-date include Cypella, Iris, Olsynium, Sisyrinchium and Diplarrena, all belonging to the subfamily Iridoideae.
The Angiosperm Phylogeny Group goes into taxonomic detail on the Iridaceae and its subfamilies.
Paghat writes about Gladiolus papilio from a horticultural perspective.