The Arizona Native Plant Society.

Cactus & Succulent field numbers, Christophe Ludwig.

CITES Cactaceae cheklist (→ Succulents).

European Nursery Catalogue Collection.

Field number query, Ralph Martin.

International Crassulaceae Network.

International Plant Names Index - IPNI.

Kew — Herbarium Catalogue.

Lingua botanica : Dictionnaire en ligne (Latin).

Mociño & Sessé biological illustrations: Cactaceae.

A Grammatical Dictionary of Botanical Latin.

SANBI - South African National Biodiversity Institute

Sulcopassion, Claude Bourleau, Sulcorebutia.

Tropicos (Missouri Botanical Garden).

Vélins du Muséum.