Crop domestication in the Compositae: a family-wide trait assessment

Despite current recognition as the largest family of flowering plants (23,000 species ± 1000; Anderberg et al. 2007), the Compositae is home to comparatively few important crop species. To assess domestication levels in the Compositae, we developed an index that categorizes taxa according to the strength of domestication. Most Compositae species that are used by humans exhibit little or no evidence of domestication and only a handful have been strongly domesticated. Although the Compositae (along with Orchidaceae) has few domesticated taxa compared to other large families such as Fabaceae or Poaceae, Compositae species have features that should make them suitable for domestication and human consumption. These include high species diversity, global geographic distribution, good seed storability, and good seed oil quality. We propose that the paucity of domesticated species in this family can be attributed to a variety of factors, chiefly the prevalence of secondary defence compounds, the lack of carbohydrates that can be digested by the human gut and the predominantly mechanical or wind-dependent seed dispersal syndrome. We also discuss the relevance of genetic and cultural factors. Although few Compositae crops currently play a major role in global agriculture, many species hold unexploited potential, especially as novel crops for food and industrial applications.