Senecio rowleyanus
String of Pearls (Senecio or Curio rowleyanus) (Jacobsen): An all-time favorite for the way its bead-like leaves can cascade several feet. They originate in South Africa where they grow as ground cover in the shade of rocky outcroppings. Partial or filtered sun is ideal, as they are prone to sunburn if exposed to direct sun without a gradual, two week transition.  Sold in single container.
 
In the wild, Senecio/Curio plants are dormant in summer and grow in winter, though this can shift under indoor growing conditions. It is a member of the Aster family and produces pom pom-like flowers that smell of cinnamon. Try growing String of Pearls in a hanging pot for a trailing effect or, in warm climates (zone 10+), plant it in-ground as a matting groundcover. For a truly bountiful trailing effect, prune and re-plant long strands.
 
The unique leaf shape is a useful adaptation that helps C. rowleyanus tolerate droughts. Its spherical form maximizes water storing volume while minimizing exposed leaf area. Having less surface area reduces water loss to evapotranspiration but it also reduces the leaf area that can absorb sunlight. To counteract this, each leaf has a translucent sliver or "window" through which extra light enters for photosynthesis.
 
PLEASE NOTE: String of Pearls is mildly toxic and can cause vomiting or diarrhea if ingested; keep out of reach of children and pets.