1. Aldridge, A. E., 1976: A critical reappraisal of the MacaronesianSonchus subgenusDendrosonchus s. l. (Compositae?Lactuceae). ? Bot. Macar.2, 25?57.
2. ?, 1977: Anatomy and evolution in the MacaronesianSonchus subgenusDendrosonchus (Compositae?Lactuceae). Nodal and petiolar vascular patterns. ? Bot. Macar.3, 41?59.
3. ?, 1978: Anatomy and evolution in the MacaronesianSonchus subgenusDendrosonchus (Compositae?Lactuceae). ? Bot. J. Linn. Soc.76, 249?285.
4. ?, 1979: Evolution within a single genus:Sonchus in Macaronesia. ? InBramwell, D., (Ed.): Plants and Islands, 279?291. ? London and New York: Academic Press.
5. Bramwell, D., 1972: A revision of the genusEchium in Macaronesia. ? Lagascalia2 (1), 37?115.