Diascia is a genus of around 70 speciesPlantZAfrica.com Diascia integerrima of herbaceous annual and perennial flowering plants of the family Scrophulariaceae, native to southern Africa, including South Africa, Lesotho and neighbouring areas.
The perennial species are found mainly in summer-rainfall areas such as the KwaZulu-Natal Drakensberg; about 50 species, mostly annuals, are found in the Western Cape and Namaqualand, winter rainfall areas.
Their common name is twinspur, in reference to the two (usually downward-pointing) spurs to be found on the back of the flower. These help to distinguish them from the similar (and closely related) genera Alonsoa and Nemesia. The spurs contain a special oil, which is collected in the wild by bees of the genus Rediviva (e.g. R. longimanus) that appear to have coevolved with the plants, as they have unusually long forelegs for collecting the oil.Google Books: Thompson, John N., The Coevolutionary ProcessPlantSystematics.org Diascia (Scrophulariaceae)
In gardens, Diascia cultivars (mostly hybrids) have become extremely popular as colourful, floriferous, easily grown bedding plants in recent years.Horticulture Week: Diascia, by Graham Clarke
Description Most diascia species are short-growing, straggling plants, reaching no more than in height, although Diascia rigescens can reach , and the rather similar D. personata (with which it is often confused)Google Books: The European Garden Flora up to or so. Some Diascia species spread by means of stolons, while others produce multiple lax stems from a single crown. The flowers are borne in loose terminal racemes. The corolla is five-lobed, and normally pink or rose-coloured in the perennial species most commonly seen in cultivation. Dark purplish patches of oil glands may make the flowers of some species appear bicoloured.
Taxonomy It was described by Johann Heinrich Friedrich Link and Christoph Friedrich Otto in 1820Diascia Link & Otto. (n.d.). International Plant Names Index. Retrieved September 10, 2025, from https://www.ipni.org/n/37587-1 with Diascia bergiana as the type species.Missouri Botanical Garden. (n.d.). Diascia Link & Otto. Tropicos. Retrieved September 10, 2025, from https://www.tropicos.org/name/40029315 Within the family Scrophulariaceae it is placed in the tribe Hemimerideae.USDA, Agricultural Research Service, National Plant Germplasm System. 2025. Germplasm Resources Information Network (GRIN Taxonomy). National Germplasm Resources Laboratory, Beltsville, Maryland. URL: https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomygenus?id=3575. Accessed 10 September 2025. Etymology Surprisingly, the generic name (from the Greek di = two and askos = bag, pouch or sack) does not refer to the spurs, but to the two translucent sacs, or pouches, known as 'windows', found in the upper part of the corolla of the original type specimen, Diascia bergiana. Diascia species in the section Racemosae have similar windows, but in some species they merge into one. The windows may help oil-collecting bees to find the correct position within the corolla when gathering oil from the glands within the spurs. Species Around 60–70 species are currently recognised in the genus Diascia:
Diascia aliciae Hiern Diascia alonzoides Benth. Diascia anastrepta Hilliard & B.L.Burtt Diascia ausana Dinter Diascia austromontana K.E.Steiner Diascia barberae Hook.f. Diascia batteniana K.E.Steiner Diascia bergiana Link & Otto Diascia bicolor K.E.Steiner Diascia capensis (L.) Britten Diascia capsularis Benth. Diascia cardiosepala Hiern Diascia cordata N.E.Br. Diascia cuneata E.Mey. ex Benth. Diascia decipiens K.E.Steiner Diascia dielsiana Schltr. ex Hiern Diascia diffusa Benth. Diascia dissecta Hiern Diascia dissimulans Hilliard & B.L.Burtt Diascia ellaphieae K.E.Steiner Diascia elongata Benth. Diascia engleri Diels Diascia esterhuyseniae K.E.Steiner Diascia fetcaniensis Hilliard & B.L.Burtt Diascia fragrans K.E.Steiner Diascia glandulosa E.Phillips Diascia gracilis Schltr. Diascia heterandra Benth. Diascia hexensis K.E.Steiner Diascia humilis K.E.Steiner Diascia insignis K.E.Steiner Diascia integerrima E.Mey. ex Benth. Diascia lewisiae K.E.Steiner Diascia lilacina Hilliard & B.L.Burtt Diascia longicornis (Thunb.) Druce Diascia macrophylla (Thunb.) Spreng. Diascia maculata K.E.Steiner Diascia megathura Hilliard & B.L.Burtt Diascia minutiflora Hiern Diascia mollis Hilliard & B.L.Burtt Diascia namaquensis Hiern Diascia nana Diels Diascia nodosa K.E.Steiner Diascia nutans Diels Diascia pachyceras E.Mey. ex Benth. Diascia parviflora Benth. Diascia patens (Thunb.) Grant ex Fourc. Diascia pentheri Schltr. Diascia personata Hilliard & B.L.Burtt Diascia purpurea N.E.Br. Diascia racemulosa Benth. Diascia ramosa Scott-Elliot Diascia rigescens E.Mey. ex Benth. Diascia rudolphii Hiern Diascia runcinata E.Mey. ex Benth. Diascia sacculata Benth. Diascia scullyi Hiern Diascia stachyoides Schltr. ex Hiern Diascia stricta Hilliard & B.L.Burtt Diascia tanyceras E.Mey. ex Benth. Diascia tugelensis Hilliard & B.L.Burtt Diascia unilabiata (Thunb.) Benth. Diascia veronicoides Schltr. Diascia vigilis Hilliard & B.L.Burtt
Coevolution with Rediviva bees
The two spurs found on the back of a Diascia flower (from which it gets the common name twinspur) contain a special oil, which is collected in the wild by at least 8 species of bees of the genus Rediviva. The bees appear to have coevolved with the plants, as the females have developed unusually long, hairy forelegs with which they collect the oil from Diascia spurs to feed their larvae (and sometimes to line their nests with). The spurs vary in average length from to as much as , mainly between species (although those of D. capsularis can vary widely between populations); the bees' forelegs vary similarly. The spurs of Diascia longicornis are about in length, but the existence of a suitably equipped pollinator, Rediviva emdeorum, with forelegs of the same length, was only confirmed in the 1980s. Rediviva longimanus has also been observed pollinating D. longicornis in the Western Cape.
Rediviva neliana, a widespread species, collects from at least 12 species of Diascia, but in general, few different Diascia species grow together in the same locality. As a result, local populations of R. neliana have been found to differ from each other, as each has developed legs that match the spur length of the diascias that are available to them in that locality. This indicates that local populations of R. neliana are coevolving with the flowers on which they depend.
Garden uses
Diascia cultivars have become extremely popular worldwide as bedding plants, suitable for hanging baskets, window boxes and other containers, as well as rockeries and the fronts of herbaceous borders. This explosion of interest is largely thanks to the breeding work done by the late Hector Harrison of Appleby, North Lincolnshire, England. From 1985, he raised hundreds of hybrid seedlings, from which several excellent cultivars have been selected and named. He increased the colour range to include shades of apricot, pink, coral, lilac, red and white. Other nurseries and breeders have continued to build on his pioneering work.
Several species and cultivars have been given the Award of Garden Merit by the British Royal Horticultural Society. The AGM includes a hardiness rating: most have been rated as intermediate between H3 (hardy outside in some regions or particular situations or which, while usually grown outside in summer, needs frost-free protection in winter – e.g. dahlias) and H4 (hardy throughout the British Isles).RHS Online: Award of Garden Merit (AGM)
Cultivars The species and cultivars commonly grown in gardens include the following (those awarded the Royal Horticultural Society's Award of Garden Merit are marked ):
'Appleby Apricot' D. barberae: 'Belmore Beauty' 'Blackthorn Apricot' H3-4 'Fisher's Flora' 'Ruby Field' H3–4 'Blue Bonnet' ='Hecbel' H3–4 'Dark Eyes' 'Elizabeth' D. fetcaniensis Flying Colours Series 'Flying Colours Appleblossom' 'Flying Colours Apricot' 'Flying Colours Coral' 'Flying Colours Red' 'Ice Cracker' 'Ice Cream' D. integerrima 'Jacqueline's Joy' 'Joyce's Choice' H3–4 'Katherine Sharman' 'Lady Valerie' H3–4 'Lilac Belle' H3–4 'Lilac Mist' H3–4 'Little Dancer' 'Little Tango' 'Pink Panther' 'Red Ace' 'Redstart' D. rigescens 'Rupert Lambert' H3–4 'Salmon Supreme' 'Twinkle' D. vigilis Whisper Series 'Whisper Apricot Improved' 'Whisper Cranberry Red' 'Whisper Pumpkin' 'Whisper Tangerine' 'Whisper White' Wink Series 'Wink Garnet'
References
External links
PlantZAfrica.com Diascia integerrima PlantZAfrica.com Diascia rigescens A UK National Plant Collection holder's website