Diastella is a small genus of seven species of flowering shrubs in the protea family (Proteaceae), order Proteales, native exclusively to the Cape Floristic Region of South Africa. They are commonly known as silkypuffs, a name that captures the distinctive appearance of their flowers: many tiny florets are crowded into compact, 10–12 mm heads that resemble delicate silky puffs. While they belong to the same family as the spectacular proteas, Diastella plants are far less imposing — low-growing shrublets and ground covers with slender, hairy stems, fine linear leaves, and mats that may spread up to 3 metres in diameter. They are distinguished from the closely related pincushions (Leucospermum) by having four free, separate perianth segments rather than fused ones.
All species are restricted to fynbos habitats, growing in the deep, well-drained, sandy, acid and nutrient-poor soils characteristic of the Cape Flats and surrounding mountains. Their range is extremely limited even within the Cape Floristic Region, and most species depend on a natural fire cycle for seed germination. Seeds are dispersed by ants and rodents, and germination is strongly promoted by fire.
Most species are threatened; several, including Diastella proteoides (Flats silkypuff), carry Critically Endangered status as their Cape Flats habitat has been almost entirely converted to housing and agriculture. Other members of the genus include Diastella divaricata (Peninsula silkypuff) and Diastella thymelaeoides (Steenbras silkypuff).
Etymology
The genus name Diastella is derived from the Greek diastellein, meaning "to separate". It refers to the four free, separate perianth segments of the flowers, which distinguish these plants from the closely related Leucospermum (pincushions), whose similar-looking segments are fused.
Distribution
Diastella is endemic to the Cape Floristic Region of South Africa, with all species confined to the Western Cape province. Individual species occupy very restricted ranges: D. proteoides is limited to the Cape Flats from Tokai eastwards to Eerste River and Paarl and northwards to Mamre; other species are similarly localised around the Cape Peninsula, Franschhoek, Tulbagh, Hangklip, and the Palmiet River area. All occur in fynbos on sandy, acid soils.
Ecology
Diastella species grow in deep, well-drained, sandy, nutrient-poor, acid soils under full sun in a Mediterranean climate with winter rainfall and dry summers. Seed dispersal is aided by ants (myrmecochory) and rodents. Seeds germinate strongly in autumn following fire, and a regular burning cycle with sufficient recovery periods is essential to the genus's reproductive biology. The plants are susceptible to a range of protea fungal infections when conditions are warm and humid.
Conservation
Most Diastella species are threatened; several are assessed as Critically Endangered (CR) on the IUCN Red List, including D. proteoides, D. buekii, D. myrtifolia, and D. parilis. The primary threat is habitat loss: the Cape Flats, which once supported large populations of D. proteoides, have been extensively developed for housing and agriculture. In-situ conservation in managed heritage areas and nature reserves is considered the most effective approach; ex-situ nursery cultivation has proved difficult due to the plants' susceptibility to fungal disease and their requirement for dry, nutrient-poor conditions. Seed banking (e.g. the Millennium Seed Bank at Kew) is used as insurance against extinction.
Propagation
Diastella proteoides is propagated mainly from heel or tip cuttings taken in spring or autumn, treated with rooting hormone for semi-hardwood cuttings and placed in a medium of equal parts milled pine bark and polystyrene pellets under mist or bottom heat. Success rates of 30–50% have been achieved. A sandy, well-drained, acid potting medium and regular organic (seaweed-based) feeding are recommended once rooted. Seed propagation is rarely practised due to difficulty of collection; if used, seeds should be dusted with fungicide and sown in late summer or autumn. The genus is considered challenging in cultivation outside its native habitat.
