Detail view - Sempervivum (commonly known as "Hen and Chicks") comes in a number of different varieties. They ordinarily propagate through larger, more mature plants producing clusters of offshoots - hence the name "Hen and Chicks."
The plants can last for several years without blooming. Age, mileage, or stressful conditions will eventually provoke a mature plant to produce a flower stalk. The stalk can vary from a short stub to as much as a foot, terminating in a cluster of small pink to white intricate blossoms.
Once they bloom and set seed, the plant dies. You'll never see the same one twice.