Ceratostigma abyssinicum (Hochst.) Asch.

This East African species is the most tender Ceratostigma. A compact shrub, it has stiff, bristly-edged leaves, more elongated than diamond shaped. Flowers of cultivated forms range from pale to bright blue. A garden plant in its native range (Cameron 2017), it is usually grown in the frost-free greenhouse or conservatory in our area. It is in the Californian nursery trade, suiting milder coastal areas. Elsewhere, it could be tried in the warmest garden microclimates, either coastally or in urban heat islands.

This plant first came to scientific attention when the British egyptologist Henry Salt collected it in the Ethiopian Highlands, in 1809–10 (Prain 1906). In 1842 the German cleric and botanist Christian Hochstetter used it as the basis of his genus Valoradia, which later workers have considered synonymous with Ceratostigma. Unlike the Asiatic species, the glands on the stigma are sessile rather than being on the horn-like protruberances which give the genus its name. Prain (1906) also described C. speciosum from Somalia, differing from C. abyssinicum in its larger flowers, scandent stems, broader leaves and denser hairs. Plants like this are now usually included within the range of variation of C. abyssinicum (Wilmot-Dear 1976, Royal Botanic Gardens, Kew 2021).