The seed is black and locally known as "Skalora sewda". It germinated readily and one specimen flowered in 6 weeks. I have identified the species as Guizotia abyssinica (L. fil.) Cass., Dict. Sci. Nat. 59: 248 (1829).
Being 20-30cm high, the cultivated plants are dwarfs compared to the size that normal plants grow in East Africa - up to 2 metres. Probably the prefer warmer climate and better results may have obtained if sown in Apr-May so as they find themselves home in our Summer.
It is closely related to Eclipta [ ] in the keys of the FLora Europaea - here's a description of the plant (op. cit.):
Stems up to 2 m, erect, divaricately branched, glandular-hairy above.
Leaves 3-10 cm, oblong lanceolate, serrate to subentire, sessile, amplexicaul.
Capitula with 5 outer involucral bracts - ovate to ovate-lanceolate, the inner hairy.
Ligules 11-15 mm, usually 8.
Achenes c. 4 mm, widened upwards, shining brown or black.
Cultivated for the oil obtained from the achenes and for bird-seed.
Casual in most parts of Europe and locally naturalized. [Cz Ge Hs It.] (E. Africa.)