With theconstant flow of plant species that reached Europe inthetimes of the great expeditions th th inthe 18 and 19 century,the demandf for anyf form of cataloguing thesteadily growingdiv- sity became unevitable. Succulent plants always fascinated plant-loving people above average, th and the first handbooks devoted to succulents were publishedin the19 century. Initially, h- ever,interest was focussed on the Cactaceae. It was only in 1954/55 when Herman Jacobsen (1898 - 1978), the former curator of the Botanic Garden of Kiel,madeavailablea first handbook devoted to succulents (excl. Cactaceae),the "Handbuchder sukkulenten Pflanzen". An abridged version of this handbook was publishedby Jacobsen as "Sukkulentenlexikon" in 1970. It included descriptions,synonymies and numerous illustrations. The"Sukkulentenlexikon" represented the long-awaited reference work supportingboth Botanical Gardens as well as amateur or prof- sionalgrowers inthe navigation through succulent plant diversity. AnEnglish edition followedin 1975 as "Succulent Lexicon", and a revised German edition was publishedin 1981.This second edition hadbeen finished by Jacobsen's successor inKiel,Klaus Hesselbarth,who,with regard to the Asclepiadaceae, was supportedby the senior editor of the present publication. Over twentyyears have passed since then, and the knowlegdeof succulent plants has increased permanently. Wesaw monographsoff formerly little-known groups and many revisions and - revisions, which often change the taxonomy withinsingle groups considerably. A large amount of new taxa has been published on one hand, and on the other hand, many taxa have been sunk into synonymy.
