Phedimus is a genus of about 18 succulent perennial herbs in the family Crassulaceae (stonecrop family), order Saxifragales, native to eastern Europe and Asia. The genus was segregated from the large, cosmopolitan and polyphyletic genus Sedum, where it had previously been treated as a section or subgenus. Within Crassulaceae it belongs to subfamily Sempervivoideae, tribe Umbiliceae, and is most closely related to the genus Aizopsis, of which it is the sister group.
Plants are typically glabrous, with stems sometimes becoming woody at the base, arising from a thin woody rhizome. Leaves are decussate or alternate, narrowed at the base, and bear hydathodes along the lower margins. Flowering branches are erect or descending, bearing dense terminal pleiochasia (multi-budded inflorescences). Flowers are 4- to 7-merous with free, usually spreading petals; sepals are typically unequal. Fruits are follicles, and seeds are costate-papillate.
The genus is recognised in two ways. In the strict sense (Phedimus sensu stricto), it comprises around five species with creeping, rooting stems and white, pink, red, or purplish flowers (chromosome base number x=5, 6, or 7). When treated more broadly (sensu lato), it incorporates Aizopsis as subgenus Aizoon — plants with annual shoots from woody rhizomes and yellow, orange, or reddish flowers (x=8). The two subgenera differ also in distribution: subgenus Phedimus ranges from the Mediterranean to the Caucasus, while subgenus Aizoon is centred in China, Japan, Korea, and central Siberia.
Phedimus kamtschaticus (widely known under its synonym Sedum kamtschaticum) is the best-known member in cultivation, grown as a low ornamental ground cover and recognised with the Royal Horticultural Society's Award of Garden Merit. Phedimus spurius (formerly Sedum spurium) is similarly popular in rock gardens and as ground cover across temperate regions.
Distribution
The genus ranges across eastern Europe and Asia. The narrow-sense subgenus Phedimus extends from the Mediterranean basin to the Caucasus region, while subgenus Aizoon (or the separate genus Aizopsis) is distributed across China, Japan, Korea, and central Siberia.
Cultivation
Phedimus kamtschaticus (syn. Sedum kamtschaticum) is widely grown as an ornamental ground cover in temperate gardens and has received the Royal Horticultural Society's Award of Garden Merit. Phedimus spurius (syn. Sedum spurium) is another popular species used in rock gardens. As members of Crassulaceae, these plants are succulents tolerant of poor, well-drained soils and full sun, making them suitable for dry gardens, green roofs, and border edges.
Taxonomy Notes
Phedimus was carved out of the broadly circumscribed, polyphyletic genus Sedum and placed in tribe Umbiliceae within subfamily Sempervivoideae of Crassulaceae. Its closest relative is Aizopsis, from which it differs in flower colour (pink or white versus yellow), floral morphology, distribution (Eurasia versus primarily Asia), and chromosome numbers (x=14 versus x=16). The boundary between the two genera remains contested: some authors merge Aizopsis into Phedimus as subgenus Aizoon, yielding a broader genus of roughly 18 species, while others maintain them separately, restricting Phedimus to about five species with creeping stems and pink or white flowers.
