Not knowing for sure the genus and species of a cactus takes away some of the fun for me. I just have a burning need to know the botanical and common names of all my specimens—perhaps Maybe I have a need to show off—or maybe by knowing the genus and species, I will know when to expect blooms and how to care for it. Different cacti, depending on their origin, have different care needs. Many maybes here!
Maybe I should actually call the Lobivia grandiflora Echinopsis grandiflora. Echinopsis, Lobivia, Soehrensia, and Trichocereus had always been classified separately, but now they are all grouped into the Echinopsis genus. However, many collectors still like to refer to the old genus. The genus, Echinopsis, is native to South America.
I think all this confusion points out to the need for accurate labeling. I label all my potted cacti, succulents, and even some of the specimens in the garden—no exceptions. (The cactus discussed above lost its label last year in a windstorm and look at the confusion!) By labeling, I know when I acquired the cactus, what genus and species it is, and how to care for it based on a code developed by the Tucson Cactus and Succulent Society. I put the code right on the label with the rest of the information, and then group the specimens by code. It works well, satisfies my anal-retentive tendencies, and makes for good horticultural practice.
Regardless of what genus and species this specimen falls under, the flowers are gorgeous!