in North America, Europe, Africa (Algeria) and in northern Asia (Cypripedium) as well as in subtropical and tropical Southeast Asia (Paphiopedilum). They do not occur in Australia and Africa. The spread could have started from a center of origin in Central America. Taxonomy Unlike most other orchids, slipper orchids have two fertile anthers — they are "diandrous". For that reason, experts have debated whether this clade should be classified within the orchid family (Orchidaceae), or whether they should compose a separate family altogether called Cypripediaceae. Around the year 2000, molecular phylogenetics and DNA sampling have come to play an increasingly important role in classification. This has led to the conclusion that recognition of a distinct family Cypripediaceae would be inappropriate. The subfamily Cypripedioideae is monophyletic and consists of five genera: Cypripedium, found across much of North America, as well as in parts of Europe (one species), Africa (only in Algeria has been discovered in 2019) and Asia. The state flower of Minnesota is the showy lady's slipper (Cypripedium reginae); the pink lady's slipper (Cypripedium acaule) is the official flower of the Canadian province of Prince Edward Island. Mexipedium, a monotypic genus, consisting of a single species that was found in a single locality in Oaxaca, Mexico. Paphiopedilum, found in the tropical forests of southeast Asia reaching as far north as southern China. Paphiopedilum is quite easy to cultivate and therefore is popular among orchid enthusiasts. In fact, over-collection of this genus has been so extensive that many species are now sub-viable in their natural habitats. Phragmipedium, found across northern South and Central America, is also easy to cultivate as it requires lower temperatures than Paphiopedilum, eliminating the need for a greenhouse in many areas. Selenipedium, found in Central and South America. Intergeneric hybrids Hybrids between the genera in this subfamily are placed in the following nothogenera: × Cyphiopedilum (Cphd.) = Cypripedium × Paphiopedilum × Cyphragmipedium (Cgd.) = Cypripedium × Phragmipedium × Phragmipaphium (Phrphm.) = Paphiopedilum × Phragmipedium Hybrids with genera outside of the subfamily are not known as of 2017. References Further reading Cox, A. V., A. M. Pridgeon, V. A. Albert, and M. W. Chase. 1997. Phylogenetics of the slipper orchids (Cypripedioideae: Orchidaceae): nuclear rDNA ITS sequences. Plant Systematics and Evolution 208: 197–223. Abstract Pridgeon, A. M.; Cribb, P. J.; Chase, M. W. & F. N. Rasmussen (1999): Genera Orchidacearum Vol. 1, Oxford U. Press. External links The Slipper