The principal difference between wild and domesticated forms of C"henopodium" is the thickness of the seed coat. In the domesticated varieties, due to selective pressures during domestication, the testas are less than 20 microns thick; the testas of wild chenopods are 40 to 60 microns thick. This morphological characteristic is shared by the modern cultivated chenopod "C. b." subsp". nuttalliae" and the archaeological specimens of "C. b." ssp". jonesianum." Genetic studies have shown that eastern North American and Mexican cultivated forms have considerable genetic distance between them. Despite the initial assumption of a single domestication event, consensus in the field now supports at least two independent domestication events in North America. Similarly, "C. berlandieri"'s South American branch likely experienced at least two independent domestication events, both of which are called "C. quinoa."