Cleistocactus strausii
Silver Torch cactus can thrive in low-nitrogen soil without facing the consequences of low nitrogen. Too much water will make the plant weak and lead to root rot. 
Least Concern. This cactus is locally abundant in its native land and has few local threats to its survival.
This cactus can be propagated by cuttings or seed.
Pilosocereus robinii
This cactus grows in upland tropical hardwood hammocks on limestone or coral substrates. It sometimes grows on sparsely vegetated coral rock and just above the high tide mark. Storm surges and sea level rise may inundate its shoreline habitat and increase the salinity beyond the tolerable range for the cactus.