Pseudolithos cubiformis

This uniquely shaped succulent isn't one you're likely to come across at your average plant store. Its cube-like shape and scaly texture are unusual in the world of houseplants and succulents, and make it desirable in the plant collector world.

But, this plant's slow-growing cycle and complex care needs make it even rarer to come across.  

"Typically, the smallest specimens will go for $75 to $125," Oakes says.