Euphorbia antisyphilitica (Candelilla, Wax plant). Full sun. Hardy to 25°F. Evergreen shrub to 3' tall, mostly leafless stems. Little water. Native to Chihuahuan desert, west Texas, Mexico.
Euphorbia horrid. The ones being sold are silver, not green as pictured.
Euphorbia resinifera (Moroccan mound); USDA: 9-11. Full sun to light shade. Hardy to 22°F. Spiny shrub to 4' tall; 6' wide. Moderate water summer. Native to Morocco.
Euphorbia tirucalli (Pencil bush). Sunset: 13, 23, 24, USDA: 10-12 Full sun to light shade. Hardy to 28°F. Succulent bush to 20' tall; Moderate water summer for fast growth. Milky corrosive sap. Origin: Africa.
Pedilanthus macrocarpus (Lady slipper) USDA: 9-10. Full sun to light shade. Little to moderate water. Hardy to 25°F. Evergreen bush to 5' tall; 6' + wide. Origin: Mexico (Sonora, Baja California).