International Code of Botanical Nomenclature (ICBN), Vienna Code (2006)
International Code of Botanical Nomenclature (ICBN), St. Louis Code (2000)
International Code of Botanical Nomenclature (ICBN), Tokyo Code (1994)
Botanical Garden Information System
International Plant Names Index (IPNI)
Cok & Ine Grootscholten: Succulents collection
Michal Susser: Haworthia (cz)
Pasquale Ruocco: Haworthia, Aloe & Gasteria
Julia Etter & Martin Kristen: Agavaceae data base
Jakub Jilemicky: Haworthias & Gasterias
Lithops – Flowering stones
Southern African Bulb Group
Claude Bourleau: Sulco-Passion (en, fr)
B & T World Seeds
Cono's Paradise (Conophytum, Lithops, Mesembs)
Exotica - Botanical rarities (Caudex plants)