at risk from habitat destruction, the International Union for Conservation of Nature (IUCN) lists ten of the eleven species in a vulnerable category on their Red List. One species, D. caputoi, is considered to be critically endangered, three as endangered (D. holmgrenii, D. sonorense and D. tomasellii) and five as vulnerable. (D. califanoi, D. merolae, D. purpusii, D. rzedowskii and D. spinulosum). D. edule is listed as a kind of "near-threatened" list. For D. mejiae, there is not enough data for an assessment of the hazard. Locations are destroyed primarily by clearing and reclamation of the land. Dioon species are also very popular with international collectors. Plants are dug up and sold. According to a report from the 1992 Washington Convention on Biological Diversity, trade with D. edule individuals reached a level of about 5,800 copies, with D. spinolosum 1,600 - this does not include illicit trade. Another potential threat to the genus is the lobster louse (Diaspididae) Aulacaspis yasumatsui. The insect originally comes from Southeast Asia and infests there cycads. The pest has now been introduced to Florida, California, India and the UK, where it causes major damage to cycads. There he was also found at D. edule. If the species were to penetrate Central America, it could drastically reduce or even destroy the populations of Dioon in a short time. Taxonomy The first description was made in 1843 by John Lindley as Dion. The genus name was given due to the two ovules per megasporophyll: Dioon comes from the ancient Greek prefix δι- di- (= two) and ώόν ōión, ōón (= egg). The leaf-like character of Sporophylle gives Dioon a special position within the cycads. Dehgan & Dehgan described the genus as the most primitive of the cycads and suggested they put them into their own family. A molecular genetic study of the chloroplast DNA revealed that it is at least the most primitive genus of neotropical cycads. Classification Classically, the family of Zamiaceae is divided into two subfamilies with four tribes. Dioon is the only genus in the tribe of the Diooeae, which together with the Encephalarteae forms the subfamily of Encephalartoideae. This classification was based on morphological considerations. A morphological study of relationships in fossil and extant taxa revealed the following cladogram: A molecular biology analysis of a fragment of 26S ribosomal DNA revealed a somewhat similar cladogram that would dramatically alter the structure of Zamiaceae.