Cumulopuntia pentlandii Family: Cactaceae. Also known as Tephrocactus pentlandii. A tiny South American cactus related to Opuntia. The stems are green and egg shaped with a few spines. Makes bright yellow flowers in the summer. Segments are 1/2" diameter or less. Easy to grow. Give good light, water when nearly dry and protect from frost.
You will receive a plant shown in the last image or one similar. It is shown growing in a 2" pot.