Sui generis
Sui generis (; ) is a Latin phrase that means "of its (his, her, their) own kind; in a class by itself; unique."
Succulent plant
Those who grow succulents as a hobby use the term in a different way to botanists. In horticultural use, the term "succulent" regularly excludes cacti. For example, Jacobsen's three volume "Handbook of Succulent Plants" does not cover cacti, and "cacti and succulents" is the title or part of the title of many books covering the cultivation of these plants. However, in botanical terminology, cacti are succulents. Horticulturists may also exclude other groups of plants, e.g., bromeliads. A practical, but unscientific, horticultural definition is "a succulent plant is any desert plant that a succulent plant collector wishes to grow." Such plants less often include geophytes (in which the swollen storage organ is wholly underground) but do include plants with a caudex, which is a swollen above-ground organ at soil level, formed from a stem, a root or both.