Research Communications Patterns of Variation in the Seed Morphology of Iva annua var. macrocarpa, an Extinct North American Domesticate Andrew W. Weiland1* and Kristen J. Gremillion1 1Department of Anthropology, The Ohio State University, Columbus, OH, USA *[email protected] 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. Received May 26, 2017 OPEN ACCESS Accepted December 12, 2017 DOI 10.14237/ebl.9.2.2018.990 Keywords Paleoethnobotany, Seed morphology, Archaeology, Native North America, Domestication Copyright © 2018 by the author(s); licensee Society of Ethnobiology. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International Public License (https://creativecommons.org/licenses/by-nc/4.0), which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Supplementary Files available at ojs.ethnobiology.org/index.php/ebl/article/view/990 Introduction Yarnell 1972; Yarnell 1981), quickly surpassing While Volney Jones and Melvin Gilmore were the maximum wild dimensions (4.5 mm) in the Late first scholars to present strong evidence for the Archaic period (5000 to 3000 BP) and increasing “Eastern Agricultural Complex” (EAC) originally gradually thereafter. proposed by Linton (1924), Richard A. Yarnell This study builds on Yarnell’s legacy of using seed pushed this research forward by accumulating a large morphology to detect overall patterns in the paleoethnobotanical database in which he was able to domestication process. However, whereas Yarnell was identify patterns across time and space. As part of this primarily concerned with the effects of natural effort, he adopted the procedure of regularly selection on average seed and fruit size under measuring seeds and fruits to identify morphological domestication, we focus instead on variation in these correlates of domestication in plants native to eastern traits. As Yarnell (1981) notes, there are some North America. Yarnell used average lengths of exceptions to the trend of increasing mean achene achenes (the dry fruit type characteristic of the aster size. Rather than being considered problematic, family, Asteraceae) from the handful of sites available however, these anomalies can be used to better at the time to demonstrate the domesticate status of understand the large-scale cultural behavior that drove the weedy annual marshelder or sumpweed (Iva annua selection in prehistoric gardens and fields. For L.; in its domesticated form known as I. annua L. var. example, phenotypic variability in traits such as seed macrocarpa [S.F. Blake] R.C. Jackson). Marshelder size is expected to decline as the gene pool of the achene size increased over time in eastern North domesticate becomes increasingly isolated from that America (Blake 1939; Jackson 1960; Smith et al. 1992; of the parent population, but ongoing hybridization Weiland and Gremillion. 2018. Ethnobiology Letters 9(2):75–89 75 Research Communications Figure 1 Map of select sites discussed and their accompanying geophysical regions. Blue=Ozark Plateaus, Green=Central Lowlands, Purple=Interior Low Plateau, Orange=Appalachian Plateau sites, mostly located in the Cumberland Escarpment. (Basemap: National Geographic, -i cubed 2013) may interfere with this process (Allaby 2010). In volume of the Journal of Ethnobiology in 1981, and more contrast, imported seedstock might be highly uniform can be said using quantitative methods to analyze morphologically when first introduced, with these measurements. We use statistics to examine subsequent gene flow dependent upon human agency. trends in average marshelder achene dimensions over To explore this variability, we analyze data from time to further characterize the patterns identified in Central Lowland sites in central and southern Illinois, Yarnell’s work (1972, 1981). We also consider the Ozark Plateaus sites in Arkansas and Missouri, effects that reproductive isolation of a small initial Interior Low Plateaus sites in Kentucky and gene pool might have had on the rate of change and Tennessee, and Appalachian Plateau sites, mostly range of variation in achene dimensions. These from the Cumberland Escarpment in Kentucky patterns may be useful for differentiating between (Figure 1). In doing so, we can take advantage of the cases of in situ gradual domestication and reports, notes, and publications that have introduction of imported seedstock into new accumulated since Yarnell wrote his piece on locations. sunflower and sumpweed achene size in the first Weiland and Gremillion. 2018. Ethnobiology Letters 9(2):75–89 76 Research Communications Seed and Fruit Morphology of Iva annua domesticated at a mean of 4.0–4.2 mm long in an Seed morphology can provide domestication archaeological context. researchers with much-needed information about the The earliest evidence of wild marshelder in an rates of change, patterns, and diffusion of archaeological context comes from the Titterington domesticates (Fuller et al. 2012; Gremillion 1993; phase of the Koster Site in the Illinois River valley and Harlan et al. 1973; Mueller 2017; Smith 1985; Yarnell dates to 6055 cal BP (Asch and Asch 1978). Mean 1981). Phenotypic change observed in length and width for these achenes fall well within the archaeobotanical evidence represents the genetic wild size range (2.3 x 1.9 mm, n length=284, n biophysical imprint resulting from the selective width=340) and well below the domesticate cutoff of environment created by long-term human adaptive 4.0–4.2 mm. Other early examples from Illinois strategies. Tracking this domestication process include the Cahokia Interpretive Center Tract (ICT) through morphological changes in the phenotype site (3321 BP) (Nassaney et al. 1982), and Titus creates a window through which archaeologists can Horizon 2 (3335 BP) (Asch and Asch 1978). These view the selective pressures created by prehistoric findings indicate that free-living marshelder was populations’ interactions with plants. Researchers present locally in the Central Lowlands, as it is today, have undertaken analyses of this kind for several of a frequent colonizer of disturbed floodplain soils and the native crop plants known as the EAC. Several of anthropogenic habitats (Asch and Asch 1978; Smith these plants exhibit traits characteristic of the adaptive 1992). syndrome of domestication (Fuller 2007; Harlan et al. The earliest evidence for domesticated marshelder 1973), such as increased seed and fruit size and is from 44 achenes from Feature 20 at Napoleon reduction of structures that inhibit germination Hollow, dated to 3920 ± 40 cal BP (Smith and Yarnell (Gremillion 1993; Mueller 2017; Smith 2006; Yarnell 2009). These specimens averaged 4.2 mm in length. 1972). Seed size is believed to be under relatively Domesticated marshelder achenes at Napoleon strong selection in human-modified habitats because Hollow and Riverton (3370 ± 40 cal BP) sites in of competition between seedlings that favors rapid Illinois predate its first appearance on the Appalachian germination and large reserves of food for early Plateau of eastern Kentucky, which comes from the growth (Harlan et al. 1973), and the differing selective Hooton Hollow rock shelter and has been directly effects of germination in the richer, less risky dated to 3315 cal BP (Gremillion 1996). The scarcity environments created by anthropogenic landscapes of marshelder in modern Appalachian Plateau flora and agroecosystems (Leishmann et al. 2001). (Black 1963, Cowan 1985) and the lack of wild-size Among the EAC crops that demonstrate this marshelder from archaeological collections suggest trend is the weedy annual marshelder, which was that human intervention brought marshelder to the most likely grown for its protein-rich oily kernels. Appalachian Plateau, already in domesticated form. Over 50 years of study has demonstrated that Black (1963) and Cowan (1985) claimed that there selection for larger kernels and surrounding achenes were no modern wild stands in Kentucky. But, these took place under human influence between roughly publications predate electronic sources such as the 3620 and 600 years cal BP. The domesticated form of USDA PLANTS (USDA, NRCS 2017) website and marshelder declined in human use in the Late many plant guides using updated surveys. While such Prehistoric around 600 cal BP, eventually