Semponium 'Sienna' is a pioneering intergeneric cross between Aeonium and Sempervivum. It is the first officially recognized cross between these genera. Semponium 'Sienna' has a spectacular colour change: bright red from spring to autumn, green-purple in autumn to early winter and dark burgundy in late winter. 'Sienna' has a compact size and grows to about 40 cm high and 40 cm wide. It grows into a nice dense, cone-shaped plant as it matures. One head produces an average of 12 offsets. The rosettes are large and strong, and the leaves are thick, firm and glossy. The plant has been bred by Mark Lea and Daniel Michael from England and is protected by plant breeders' rights. The entry was made by F.N. Kempen from Mijdrecht, which also markets the plant. Management is through Plantipp BV from IJsselstein.