String of Pearls, Senecio rowleyanus
String of pearls is an unusual succulent with nearly spherical leaves from South Africa. Named after British botanist Gordon Rowley, the species was recently moved from huge genus Senecio (which contains not just succulents but also common weeds like common groundsel) into the new genus Curio, but is likely to be identified as Senecio rowleyanus in literature and the horticulture trade. This tender evergreen perennial in the daisy family (Asteraceae) is native to dry areas of the eastern Cape of South Africa. There is also a variegated form with wide white stripes and sections (which might actually be S. herreianus which has slightly larger, elongated and striped round leaves and is also called string of pearls or string of beads).
The small leaves are the size and shape of small peas.
The plant grows from weak surface roots, producing trailing stems up to three feet long on the ground which can root where they touch soil to form dense mats. It often grows under bushes or between rocks which provide some protection from intense sunlight. The alternate, water-storing leaves are the size and shape of small peas (each to 1/4‚Äù diameter) with a small pointed tip on the end and a thin stripe of dark green along the side. The round shape of the leaves minimizes the surface area exposed to dry desert air and therefore reduces evaporative water loss but also reduces the surface area where photosynthesis can occur compared to a normal thin, flat leaf. The ban of darker, translucent tissue on the side of the leaf is an ‚Äúepidermal window‚Äù which allows light to enter the interior of the leaf, effectively increasing the area available for photosynthesis. This adaptation to arid environments is seen in several other succulents from southern Africa, including the related Senicio radicans, and in baby toes (Fenestraria spp.) and Haworthia cooperi which grow underground, exposing only the leaf tips.