I think that current state of recovery plan for one of the most popular and most beautiful cacti can be an interesting lecture. ;)
Species profile on U.S. Fish & Wildlife Service:
http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=Q07V
Plan itself (2003):
http://ecos.fws.gov/docs/recovery_plan/031106.pdf
Current(!) implementation status:
https://ecos.fws.gov/roar/pub/planImplementationStatus.action?documentId=100012&entityId=513
I also attached an article about in vitro culture and its meaning for plant recovery in this topic:
https://www.cactuscultivars.com/forum/index.php?topic=770.msg4992#msg4992
;D