Sunflowers (Helianthus spp.) are plants native to the American continents, and one of four seed-bearing species known to have been domesticated in eastern North America. The others are squash Cucurbita pepo var oviferia, marshelder Iva annua, and chenopod Chenopodium berlandieri). Prehistorically, people used sunflower seeds for ornamental and ceremonial use, as well as for food and flavoring. Prior to domestication, wild sunflowers were spread throughout the North and Central American continents. Wild sunflower seeds have been found in numerous locations in eastern North America; the earliest so far is within the American Archaic levels of the Koster site, as early as 8500 calendar years BP (cal BP); when it was precisely domesticated, is difficult to establish, but at least 3,000 cal BP.
Identifying Domesticated Versions
Archaeological evidence accepted for recognizing the domesticated form of sunflowers (Helianthus annuus L.) is the increase in the average mean length and width of achene--the pod that contains the sunflower seed; and since Charles Heiser's comprehensive studies in the 1950s, the established reasonable minimum length for determining whether a particular achene is domesticated has been 7.0 millimeters (about a third of an inch). Unfortunately, that is problematic: because many sunflower seeds and achenes were recovered in the charred (carbonized) state, and carbonization can, and in fact often does, shrink the achene. In addition, the accidental hybridization of wild and domestic forms--also results in smaller sized domestic achenes.
Standards to correct for carbonized seeds developed from experimental archaeology on sunflowers from DeSoto National Wildlife Refuge found that carbonized achenes exhibited an average of 12.1% reduction in size after being carbonized. Based on that, Smith (2014) proposed scholars use multipliers of about 1.35-1.61 to estimate the original size. In other words, measurements of carbonized sunflower achenes should be multiplied by 1.35-1.61, and if the majority of the achenes falls over 7 mm, you can reasonably surmise that the seeds are from a domesticated plant.
Alternatively, Heiser suggested that a better measure might be the heads ("disks") of sunflowers. Domesticated sunflower disks are significantly larger than wild ones, but, unfortunately, only about two dozen partial or complete heads have been identified archaeologically.
Earliest Domestication of Sunflowers
The main site of domestication for sunflower appears to have been located in the eastern North American woodlands, from several dry caves and rock shelters of the central and eastern United States. The firmest evidence is from a large assemblage from the Marble Bluff site in the Arkansas Ozarks, securely dated to 3000 cal BP. Other early sites with smaller assemblages but potentially domesticated seeds include Newt Kash Hollow rock shelter in eastern Kentucky (3300 cal BP); Riverton, Eastern Illinois (3600-3800 cal BP); Napoleon Hollow, central Illinois (4400 cal BP); the Hayes site in central Tennessee (4840 cal BP); and Koster in Illinois (ca 6000 cal BP). In sites more recent than 3000 cal BP, domesticate sunflowers are frequent occurrences.
Early domesticated sunflower seed and achene was reported from the San Andrés site in Tabasco, Mexico, direct dated by AMS to between 4500-4800 cal BP. However, recent genetic research has shown that all modern domestic sunflowers developed from the wild eastern North American species. Some scholars have argued that the San Andres specimens may not be sunflower but if they are, they represent a second, later domestication event that failed.
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