There are about 100 different Dorstenia species and maybe an untold number of hybrids! That's because this cute little bloomer will cross pollinate (if not carefully controlled) in a multiple species environment. When the seeds ripen, the little fruit (it's a stone fruit---don't eat it) pops off the small "disc" shaped flower center. The seed lands in any one of the many neighboring plants and generates a new plant. Seed can be purchased of one species but to have some fun, purchase a couple of different plants, sit them in close proximity to each other and watch what happens over time.
Dorstenia all have a smelly milky sap (characteristic of the family Moracaea....figs and mulberry). Since the native habitat is the Afrotropic and Neotropic zones, it is clear that in the Las Vegas area the Dorstenia are best suited as house plants and definitely not an "in ground" landscape plant. They require a somewhat damp soil during the warm sunny growing and blooming months. They may (probably will) go dormant in the winter. They will appreciate only a small bit of moisture when dormant (just like all plants succulents). Well drained soil and slightly tight rooting area will help protect the plant from the human instinct to over water.
Dorstenia gigas is characterized by its greenish trunk, Dorstenia foetida and Dorstenia crispa are reasonably available and often cross in the home and greenhouse environment. Click on this link to see lots of pictures of Dorstenia.
Reference material: Personal experience while working (with thanks) for Dave and Kris at Turner Cactus & Succulent Greenhouse; Personal experience while "hanging out" with Stan Korabell and Eunice Thompson at CSSSN events; Sajeva, Maurizio & Costanco, Mariangela. Succulents The Illustrated Dictionary, Portland: Timber Press, 1997. Print.; Flora Gardener's Enclyclopedia. Portland: Timber Press, 2003. Print.