Patterns of Variation in the Seed Morphology of Iva annua var. macrocarpa, an Extinct North American Domesticate

Abstract

Using measurements from archaeological achenes of the extinct North American cultigen marshelder (Iva annua var. macrocarpa [S.F. Blake] R.C. Jackson), we quantitatively explore patterns of variation of fruit length and width across mid-continental North America. Linear regression shows that while achene length and width increase significantly over time (length: p-value<0.0001, b=-126.04, r2=0.1037, width: p-value<0.0001, b=-230.85, r2=0.0964), overall, regions tend to show more variation. A high incidence of phenotypic variation among domesticated marshelder as measured by coefficient of variation may be a result of introgression with wild stands. An ANOVA Tukey post-hoc analysis of archaeological site samples resulted in homogeneous subsets which correspond to region with some overlap, interpreted as a cline. These results and the low numbers of wild-sized achenes in archaeological marshelder samples of eastern Kentucky support human introduction of domesticated marshelder into this region. Marshelder in the archaeological record reflects the long-standing mixed economies of hunting-gathering and agriculture used by indigenous communities of eastern North America.