The current state of our knowledge of the domestication and evolution of the grain amaranths: a critical standpoint.

BACKGROUND

Amaranthaceae is a large family of angiosperms consisting of the former Amaranthaceae sensu stricto and the former Chenopodiaceae, distributed from the tropics to more temperate regions. Amaranths were independently domesticated in Asia and America. For seed production, three native American species, referred to as grain amaranths, resulted from human artificial selection and cultivation over thousands of years: Amaranthus caudatus, A. cruentus and A. hypochondriacus.

SCOPE: This review attempts to provide a survey of the research in amaranths since Sauer (1918-2008). In addition, we try to clarify confusion in the literature by posing the following questions. (1) Were Sauer's proposals corroborated by recent research? (2) Is there consensus on an ancestor of the grain amaranths? (3) What is the domestication syndrome of grain amaranths? (4) Is there consensus on the domestication of grain amaranths?

CONCLUSIONS

Sauer's hypothesis that the three grain amaranths originated from a single ancestor, and that artificial selection combined with hybridization with wild species resulted in the three grain amaranths, is corroborated by most recent authors. There is consensus that the three grain amaranths originated from Amaranthus hybridus. However, it appears that A. hybridus is polyphyletic. Only seed colour is predominantly present in the literature as a character of the grain amaranths domestication syndrome. There is no consensus on the degree of domestication of the grain amaranths. In the literature, there is considerable confusion regarding terminology, the way dates are displayed, concepts and geographical locations. However, we can conclude that there is consensus about the South American Andes and large parts of Mexico as geographical origins of domestication. Without doubt, the lack of good phylogenetic hypotheses for Amaranthus also blurs each attempt to clarify the evolution of the cultivated amaranths from their wild ancestors.