Cleistocactus strausii
As a houseplant, the Silver Torch cactus is an easy to take care of so long as over-watering is avoided. To naturally simulate the porous effects of the sand in its native habitat, it's important to ensure that excess water will not pool in the soil, causing the roots to become water logged.
This plant’s native habitat does not have winter, but when temperatures drop to the low twenties, it can exhibit signs of tip frost. 
The Silver Torch cactus is most susceptible to 
mealybugs 
and spider mite.
Cypripedium acaule
For artificial cultivation container culture is a must, and the growing medium must be naturally acidic. Additionally, all other soil additives must be devoid of any calcium that could buffer the pH to above 5. High quality peat moss or pine duff work well, and pH neutral perlite can be added to improve porosity. Due to the risk of calcium bicarbonate, tap water is unsuitable. Rainwater or distilled water mixed with of vinegar per gallon will assure that a reliably high acidity is maintained in the growing medium. Give bright dappled shade or morning sun. Sink pots in winter or store in a cold frame for insulation. Given these conditions "C. acaule" can thrive indefinitely, but will always require much more maintenance than other species/hybrids that can be grown in a wider pH range.