Development and ecophysiology of amaranths

Amaranthus (Amaranthaceae) is a genus of tropical origin but widely distributed all over the world, including temperate regions. ^1,2About 50 species are native to the Americas and another 15 can be found in Europe, Asia, Africa, and Australia. Most amaranth species are pioneer nitrophilous annuals of open habitats and produce many small dormant seeds. This extensive seed production is associated with prolonged seed-dormancy and with prompt germination after soil disturbance and seed exposure to light. This assemblage of reproductive traits enables amaranths to survive by continuous colonization of new disturbed sites with full sunlight and little competition from other plants. With such strategy of reproduction it is not surprising that several species of amaranth were preadapted for invasion of habitats drastically modified by human activities. Thus, today, amaranths are best known as opportunistic weeds, associated with soil cultivation (e.g., A. hybridus L., A. powellii S. Watt., A. retroflexus L., A. spinosus L., etc.). However, other amaranth species have been domesticated in tropical and subtropical regions and are cultivated for their grain (A. hypochondriacus L., A. cruentus L., A. caudatus L. = A. edulis Spegazzini) or for leaf consumption (A. tricolor L. = A. gangeticus L., A. viridis L. = A. gracilis Desf., A. blitum L. = A. lividus L.).