Palynology and archaeological inference - Northern Arizona University

Journal of Archaeological Science 35 (2008) 2085e2101 http://www.elsevier.com/locate/jas

Palynology and archaeological inference: bridging the gap between pollen washes and past behavior Phil R. Geib a,*, Susan J. Smith b a

University of New Mexico, Anthropology Department, MSC01 1040, Albuquerque, NM, 87131, USA b Laboratory of Paleoecology, Box 6013, Northern Arizona University, Flagstaff, AZ 86011, USA Received 5 November 2006; received in revised form 22 January 2008; accepted 23 January 2008

Abstract Credible interpretation of pollen recovered from archaeological sites hinges upon understanding how pollen becomes deposited by both the environment and human behavior. The environmental role has been studied to some extent, but how the activities of people have formed the pollen assemblages at archaeological sites is usually just assumed rather than considered explicitly. Moreover, the complexity involved in the interaction between human behavior and pollen ecology is seldom considered. An archaeological case study of grinding tool pollen washes highlights the ambiguities of standard practice because the results confound common assumptions about pollen washes. A series of experimental seed and grinding tool washes designed to test the relationships between the processing of seeds and the deposition of pollen help explain why, for most situations, artifact pollen washes do not provide direct or even faithful records of plant processing. These results highlight the need for further experimental research with pollen so that we are warranted in making behavioral inferences from palynology. This conclusion is easily extended to other microbotanical data classes that archaeologists regularly employ. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Palynology; Pollen washes; Grinding tools; Maize pollen; Experimental archaeology; Food processing; Middle range research

1. Introduction Pollen analysis debuted in Southwestern archaeology in the late 1930s (Sears, 1937), but remained a novelty until the 1950s (Anderson, 1955; Sears, 1952). After an initial period of rather piecemeal application, the technique grew in popularity such that today it is standard practice. Since the 1970s, most archaeological projects have included some component of pollen analysis as a tool to infer dietary and other uses of plants (see Hall, 1985). One means of examining prehistoric plant use is by rinsing artifacts recovered from sealed archaeological contexts, especially grinding stones. Such artifact washes generally recover pollen grains, some of which are thought to have been embedded in the tools from plant processing (Hill and Hevly, 1968; McLaughlin, 1977). However, there is no critical test of this basic assumption. In * Corresponding author. Tel.: þ1 505 553 2422. E-mail address: [email protected] (P.R. Geib). 0305-4403/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2008.01.011

fact, one study relied on this assumption to define the function of a set of archaeological artifacts and refute use models based on metate size and texture (Halbirt, 1985). During the course of a multi-year data recovery project on Navajo Tribal land in northeastern Arizona and southeastern Utah (Geib and Spurr, 2007), we generated 58 pollen washes from 49 artifacts recovered from 13 of 33 excavated sites. Early in this project, we became frustrated trying to interpret past human practices from these samples. Since pollen is produced during the flowering stage of plant reproduction, why should it adhere and persist on seeds in any quantity? Does the pollen recovered from artifact washes truly reflect the plants processed in centuries past? An ad hoc account for what pollen might mean in terms of human behavior is possible, but what are the linking principles that allow such an exercise to proceed more conclusively? This question assumed more importance than forging ahead towards some narrow contract goal. It required us to stand back and explore means of resolving ambiguity. One approach is with the

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P.R. Geib, S.J. Smith / Journal of Archaeological Science 35 (2008) 2085e2101

archaeological pollen washes themselves while another, and ultimately more fruitful approach, is with middle range (experimental) research in the sense originally advocated by Binford (1977, 1978; see Arnold, 2003). We pursued both approaches simultaneously in the context of the overall data recovery project (Table 1). Our experimental findings produced some surprises and insights, but more importantly they emphasize that there is no substitute for the knowledge derived from experimental data and that further research along the lines reported here is sorely needed. 2. Palynological considerations There is a constant atmospheric rain of pollen grains composed of a mixture of species from the surrounding local to regional vegetation (scale of meters to kilometers); the

Table 1 Research outline Themes

Questions

Archaeological Case Study: The Navajo Mountain Road Project Pollen signatures from 1. Is there any relationship between different aspects of artifacts the abundance of pollen recovered from an artifact wash and the tool surface area or texture (grain size, pores, vesicules)? 2. Are there any differences in pollen assemblages between the use surface and non-use surface of a grinding tool? 3. Are there differences in the pollen spectra between the surface dust adhering to a metate use surface and deeper layers of pollen that might be embedded in the rock interstices of the use surface? 4. Can control samples help isolate distinctive signatures in pollen washes? Experimental studies Laboratory experiments (a) Pollen washes of harvested seeds (b) Pollen washes of metates after laboratory grinding of seeds (c) Pollen washes of maize husks, silks, ears and kernels

Field experiments Pollen washes of metates after field grinding of seeds

1. Does pollen persist on harvested seeds through preparation techniques such as winnowing and parching? 2. If pollen persists through winnowing and parching, would it become embedded in metate surfaces during grinding in enough abundance to be recovered in a pollen wash and correctly identified as the processed resource? 3. Considering that corn ears are tightly and completely encased in husks, why should maize pollen be present on kernels? Does husking remove maize pollen? 1. If there is a significant input of environmental pollen when grinding is conducted outside, will it swamp the signature from seed processing?

composition of this pollen rain changes with the seasons according to which species are flowering and climatic conditions. Pollination is part of the reproductive system in flowering plants that results in the transfer of male gametes contained within the microscopic structure of a pollen grain to female ova contained within the carpel presented by a flower (Fægri and van der Pijl, 1979). Pollination is mediated by two main syndromes: entomophilous or insect pollination and anemophilous or wind pollination (Fægri and Iversen, 1989). Conifers, grasses, and several shrubs (e.g. sagebrush) are wind-pollinated and produce abundant, aerodynamic pollen that can travel up to hundreds of kilometers, whereas insectpollinated plants, which include many herbs, forbs, and cacti, produce small amounts of heavy, ornamented pollen designed to hitchhike short distances on insects or remain within the parent flower. These two categories are not exclusive and some plant species employ both methods (e.g. Salix, willow). Wind-pollinated taxa are generally over-represented in pollen samples and insect-pollinated types are typically underrepresented. A single pine tree may produce more than a billion wind-transported pollen grains, whereas the herbaceous Plantago (plantain) may produce fewer than 100 pollen grains (Fægri and Iversen, 1989, p. 12). Abundance of an insectpollinated plant in archaeological contexts is potentially indicative of cultural use, but can also result from other natural vectors, such as insects (Bohrer, 1981, p. 136). Pollen grains entrained in the sediments at archaeological sites have been produced, transported, deposited, and degraded differentially by a suite of natural biological, chemical, and physical processes (Bryant and Hall, 1993; Dimbleby, 1985; Fægri and Iversen, 1989; Hall, 1991) in addition to modification of pollen assemblages due to human activities. There are no standard rules for interpreting archaeological pollen data but there are guidelines (Bohrer, 1981). The quality of palynological interpretations from archaeological sites reflects the experience and knowledge of analysts including specific knowledge of the vegetation and geomorphology around sites and the human history. The best criteria for inferring ethnobotanical resources from archaeological samples are when specific pollen taxa are overrepresented from what would be expected for natural background pollen rain (Bohrer, 1981) and when there are repetitive associations of pollen types or suites of types by context. Expectations for natural background pollen are usually derived from modern pollen samples of the local area around a site under investigation or from an environment similar to that of the site. However, we acknowledge there are problems defining natural pollen spectra from modern vegetation communities that have been modified by varying degrees of anthropogenic impacts (see Nabhan et al., 2004). Another key criterion is the occurrence of pollen aggregates, which are clumps of the same pollen type (Bohrer, 1981; Gish, 1991, p. 238). These are thought to represent flower anthers that have not released individual pollen grains (Gish, 1991), but aggregates are also formed by physical processes, such as pine pollen accumulating along the shorelines of puddles. Large and numerous aggregates in archaeological contexts are interpreted to relate to human manipulation of


plants and their presence carries seasonal implications (Gish, 1991). 2.1. Artifact washes Artifact washes are a special subset of archaeological pollen samples. The material washed from artifact surfaces is a combination of sediment and other material from the surrounding context that has become embedded in the stone tools in addition to what traces of plant processing remain on the tool surface. Typically, too few pollen grains are recovered from artifacts to define any significant statistical pollen population. The low recovery of pollen and the inherently different formation processes exclude use of modern control samples to help infer which taxa may have been processed on the tools. We explore the issue of control samples in this analysis by examining sediment encasing artifacts or closely associated with the artifact. Bohrer (1972, p. 26) demonstrated that pollen adheres to seeds, fruits, and corn husks and she outlined several factors that could influence the abundance of pollen on mature fruits and seeds. The position of the ovary (superior or inferior), whether there are sticky exudates, hairs, or bristles that might trap pollen on fruits and seeds, the order in which flowers mature on the plant (determinate or indeterminate), and the persistence of old blooms on fruits (e.g. shriveled blossoms stubbornly clinging to squash) all contribute to the amount of pollen deposited and retained on seeds and fruits. Another facet to the polleneplant dynamic is that harvested produce will contain a variety of ‘‘other’’ pollen types that have become glued or trapped on various parts (leaves, stems, flowers, and seeds). Adams (1988, pp. 614e637) showed that in some cases the pollen of other taxa predominate over the harvested species. We expand on both the architecture of plants and the contribution from other pollen types in the laboratory trials reported here and show that both topics are important to understanding the source of pollen recovered in artifact pollen washes. 3. Methods Five types of samples were processed and analyzed: sediment control samples from archaeological contexts, pollen washes of archaeological metates and manos, pollen washes of metates after experimental grinding trials, pollen washes of seeds and chaff, and pollen washes of corn kernels, ears, husks, and tassels. Extraction and analysis methods are detailed below for each type of sample. 3.1. Wild seed harvesting and pollen washes From various localities scattered across the Colorado Plateau we harvested seeds of wild plants in a 50 m radius during peak seasons: June for Indian ricegrass (Achnatherum hymenoides), July for tansy mustard (Descurainia pinnata), and September to October for the other species. We harvested most plants by hand-stripping the seed heads. Indian ricegrass

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was both hand-stripped and field-burned (Wheat, 1967, p. 11) by igniting piles of cut grass, which produced a shower of small, dark seeds. In hindsight, burning also would have effectively concentrated the seed of both palmer amaranth (Amaranthus palmeri) and dropseed grass (Sporobolus spp.), which are tightly encased (in the grass by lemma and palea and in the palmer amaranth by stiff, spiny bracts). Seeds were winnowed, parched, and winnowed again and this was done outside during January when environmental pollen was at its lowest seasonal flux. Winnowing effectively cleaned most of the seeds but those with little weight difference between seed and chaff, such as the dropseed grass, did not easily separate and this resulted in grinding a seed and chaff mix for these taxa. Sunflower (Helianthus annuus) seeds were ground inside their shells, which is consistent with the findings of coprolite studies (e.g., Van Ness and Hansen, 1996). Pollen washes were completed on measured quantities of seeds (weight and volume) after winnowing and again after parching. Tracers (Lycopodium spores) were added to samples to enable concentration calculations. Pollen was recovered from the seeds by mixing samples with hot distilled water and a 10% solution of potassium hydroxide, which acts as a dispersant. The mixture was sieved through a 0.18 mm mesh screen and the screened liquids were acetolyized, a chemical treatment that digests organic material, such as lignin, but not pollen. 3.2. Maize collection and pollen washes In all, 26 maize samples were analyzed: 15 from different portions of three ears (five each), 9 of shelled kernels, and a husked ear and a shucked cob (one lacking kernels). The 15 samples from three maize ears consisted of husks (three for each cob in sequence from exterior to interior), inner silks, and the shucked ears. These ears were collected from Navajo fields in Long House Valley of northeastern Arizona; they represent three color varieties of flour maize (white, blue, and yellow). We harvested the ears in mid-October, before the first killing frost but after the kernels were hard. In the laboratory, husks were carefully removed in sequence to create three samples of outer, middle, and inner husks for each ear. Exposed tips of any interior husks were trimmed and added to outer husk samples. Care was taken to prevent the inadvertent addition of pollen to any interior samples by handling. The interior silks and husked ears were saved as separate samples for these same three ears. The various maize samples were weighed and washed with hot distilled water and 10% potassium hydroxide. The wash liquids were collected and processed as the seed washes described above. Pollen of any type was rare in all of the different types of maize washes. Twenty-three of the 26 washes (88%) produced counts of 11 or less total pollen grains and the material on the slides was extremely clean with no matrix of other debris. Because of the clean samples and low pollen density, we completed counts for several samples at a low magnification of 100. Pollen counts were

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transformed to concentrations as the number of grains per weight of maize material washed (grains/g). 3.3. Sediment control samples Control samples for the archaeological artifacts consisted of surficial sediment adhering to artifacts, sediment from beneath the artifact, or floor sediment from contexts containing the artifact. The sediments were processed using the heavy liquid method employed by the Laboratory of Paleoecology, Northern Arizona University, prior to 1997 (the extraction procedure was significantly changed in 1997, based on experimental data (Smith, 1998) and additional refinements were added in 2000). Sediment subsamples, typically 20 cm3 but occasionally as small as 10 cm3, were spiked with Lycopodium spores. Hydrochloric acid (10% solution) was added to the sediments to dissolve caliche and carbonates, followed by sieving through a 0.18 mm mesh stainless steel screen to separate coarse sediment and other macro materials. Samples were then mixed with a zinc bromide heavy liquid (specific gravity 2.0) and the lighter particles, including pollen, were floated from the heavy inorganic fraction. Acetolysis of the light fraction was next, followed by a 10-min hot hydrofluoric acid treatment (approximately 49% solution), which dissolves silicate minerals. 3.4. Metate and mano washes, archaeological and experimental The metate grinding surfaces and use surfaces of manos were scrubbed with hot distilled water and 10% hydrochloric acid. For a select set of artifacts, separate washes were collected from the use-surfaces and the non-use surfaces for comparison. We also experimented with using dimethyl sulfoxide (DMSO), which is a penetrant and solvent, to accelerate the action of the hydrochloric acid. The retained liquids were spiked with a known concentration of tracer tablets (Lycopodium spores), sieved through a 0.18 mm mesh screen, and centrifuged. After recording the sediment volume, samples were processed with either a hydrofluoric acid treatment followed by a heavy liquid gravity separation (zinc bromide 2.0 specific gravity) and acetolysis, or only the acetolysis treatment. The difference in processing was determined by how ‘‘dirty’’ the wash liquids were; samples with abundant material (inorganic and organic) were treated with the longer procedure. The final extracted residues from all types of samplesdground stone, seed washes, and sedimentdwere rinsed with alcohol, mixed with glycerol, and stored in glass vials. 3.5. Pollen analysis methods A droplet from each vial was placed onto microscope slides, sealed with a cover slip, and examined using a Reichert compound microscope. Two levels of microscopy were used: 400 magnification counts of consecutive microscope slide transects until 200 or more grains, if possible, were tallied;

and 100 scans of the entire slide to document pollen aggregates and occurrences of rare large pollen types that may have been missed in the high magnification counts. If preservation is moderate, pollen greater than approximately 30 mm in size is easily identified at 100 magnification, including maize, squash, cacti, and some herb types. Pollen aggregates were counted as one grain per occurrence with the number and size of aggregate grains recorded separately. The seed washes generally produced minimal pollen. Pollen assemblages from seed washes were documented by counting all pollen observed during a tally of a minimum of 100 pollen grains of the processed seed (target taxon), or all the pollen encountered in a count of 50 tracer grains. Pollen identifications were made to the lowest taxonomic level possible based on published keys (Kapp et al., 2000; Moore et al., 1991) and the Laboratory of Paleoecology pollen reference collection curated at Northern Arizona University. Sunflower family pollen (Hi-Spine Asteraceae) was differentiated from the ragweed type (Low-Spine Asteraceae) based on spine height greater than 2 mm, as defined by Hevly et al. (1965). Pinyon pine was separated from other pines by grain length, based on keys developed by Jacobs (1985). Indian ricegrass (Achnatherum hymenoides) pollen identified in the modern seed pollen washes is discriminated from other grasses by grain diameters between 30 and 50 mm. In natural and archaeological pollen assemblages, this large grass type subsumes several genera including reed grass (Phragmites), ricegrass (Achnatherum hymenoides), little barley grass (Horedum), panic grass (Panicum), and the cereal grasses (e.g. wheat (Triticum), oat (Avena), and others). Three parameters were calculated from the pollen counts: taxa richness, sample pollen concentration, and pollen percentages. Taxa richness is the number of different pollen types identified in a sample. Pollen concentration, which is a measure of the density of pollen in a sample, is commonly expressed as numbers of pollen grains per cubic centimeter of sample sediment (abbreviated as grains/cm3). Concentrations are used to emphasize differences between samples, whereas percentages smooth data by normalizing sample populations to 100 ([taxon count/pollen sum] 100). Generally, palynologists prefer to represent pollen counts as percentages because the data are smoothed; the pollen count in each sample is normalized to 100 (taxon count divided by the pollen sum multiplied by 100). However, percentages mask differences between samples, a bias called the Fagerlind effect (Fagerlind, 1952), because relative frequencies do not reflect differences in the absolute abundance or density of pollen grains between samples. Another disadvantage is that percentages are not related to sample size. We were most interested in the abundance or density of pollen, which can be estimated by pollen concentration; however, it is difficult to derive a measure of pollen concentration from artifact washes because there is no consistent sample size to relate the pollen counts to. For the artifact washes, we calculated pollen concentration two ways: (1) based on the volume of material (primarily sediment) documented after the first centrifuge step during processing, expressed as grains/cm3 (grains per cubic


centimeter of centrifuged sediment); and (2) based on artifact use-surface area, expressed as grains/cm2 (pollen grains per cm2 of artifact surface). Pollen concentration for the sediment samples was based on the standard 20 cm3 sample volume and was calculated by taking the ratio of the pollen count to the tracer count and multiplying by the initial tracer concentration. Dividing this result by the sample volume yields the number of pollen grains per cubic centimeter of sample sediment (grains/ cm3). Pollen concentration from the seed washes was calculated from the weight of seeds washed and is expressed as the number of pollen grains per gram of seeds (grains/g). 3.6. Plant names Discussion of plants and pollen types entails botanical names, which can be confusing, and the topic is further complicated because pollen and plant names are not directly equivalent; pollen types typically subsume several plant species and genera (Table 2). Also the botanical scientific nomenclature is perpetually under construction as species are re-evaluated, and the pace of taxonomic change has increased with the advent of DNA studies. We therefore discuss the results using common names for plants and pollen types; we provide both common and scientific names in tables where appropriate. The reference for the current accepted scientific plant names is The Plants Database (USDA, 2006). 4. Archaeological case study For the research presented here we use a subset of pollen washes from the Navajo Mountain Road archaeological project consisting of 10 metates, 16 small (one-hand) manos, and 14 large (two-hand) manos (Table 3; detailed results are presented in Smith and Geib (2007)). All of these tools are of sandstone exhibiting a range of grain sizes and vesicularity, texture variability that clearly seems to play an important role in pollen recovery as discussed below. There are several artifact-related variables that might have an important bearing upon how to interpret pollen wash assemblages. When pollen and sediment accumulate on a surface, the size or area of the surface would seem to be a critical variable controlling the amount of material. Texture too should be important, in that a rough surface with much topography, especially numerous pores or vesicles, should work to trap and preserve more pollen. Vesicles are pockets and small holes in the natural fabric of the rock (Fig. 1) that in effect increase the surface area of a tool. Assuming that seed grinding leaves a pollen signature that can be recovered and correctly interpreted, then artifact washes should produce assemblages distinct from other kinds of samples. We explored these issues with the basic questions outlined in Table 1. 4.1. Pollen abundance and artifact attributes We predicted that the larger the use surface of an artifact the more material, including pollen, would be recovered in a pollen wash. In Fig. 2, the volume of sediment recovered

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in pollen washes is plotted against the surface area of the artifacts; in Fig. 3, pollen concentration, calculated as grains/ cm3, is plotted against the artifact surface area. The three artifact classes (one-hand manos, two-hand manos, and metates) are depicted in the graphs with separate symbols and are arrayed along the x-axis from smallest to largest. There is no definitive trend in the amount of sediment recovered by surface area (Fig. 2), and in fact, there is a cluster of six small manos that yielded more sediment than most of the metates. However, there is a weak trend for a greater abundance of pollen from the larger artifacts (Fig. 3). Perhaps some of the variance in the productivity of pollen washes is the extent to which the artifacts were protected from ambient pollen during use or final deposition. For example, a metate left outside, especially with the use-surface turned up and open to environmental pollen rain, would be expected to capture and preserve more pollen than an artifact stored in a protected context such as a structure interior. But comparison of contexts between the artifacts analyzed in Figs. 2 and 3 revealed this not to be the case. Tools recovered either from protected contexts, such as inside a structure or pit, or from an extramural context, such as an activity area, produced both high and low pollen concentrations (grains/ cm3 or grains/cm2) without any predictable pattern related to the context. When considering the physical attributes of the grinding tools, there is some dynamic correspondence between artifact texture and pollen density. Analysis of the grinding tools documented their texture by two separate variables: grain size and vesicularity. The former used the Wentworth scale to assign tools to one of seven categories ranging from silt to conglomerate; many tools had a medium (0.25e0.5 mm) or coarse (0.5e1.0 mm) grain size. Rock vesicles were coded as absent, sparse or abundant with further specification of pore size (small (3 mm)). The key separation was between sparse and many vesicles. Fig. 4 shows that the highest pollen concentration values were recovered from artifacts with the highest ranks for vesicles, those with many regardless of actual pore size (4þ). The coarsest-grained manos and metates also tended to produce high pollen concentrations, even if the rocks lacked abundant vesicles. Thus, the most important characteristic for trapping pollen on an artifact surface is texture, especially vesicles. It is important to note that all of the grinding tools considered here are of sandstone but the range of textures fully capture all but the smoothest grinding tools such as those made of a dense limestone. 4.2. Multiple pollen washes from the same artifact Any direct link between prehistoric plant processing and artifact pollen washes should leave distinct pollen signatures on use-surfaces that would contrast with non-use surfaces. Along this same vein, it is possible that lab personnel performing pollen washes are generally collecting the superficial surface sediment from artifacts and may be missing potential cultural signals embedded deeper within the rock pores and interstices, or at least confusing a cultural signal with extraneous pollen

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Table 2 Pollen types commonly identified from archaeological sites of the Colorado Plateau Pollen taxa

Common name

Pollination mode

Apiaceae

Parsley family includes spring parsley (Cymopterus), water hemlock (Cicuta), osha (Ligusticum), and others Sunflower family includes rabbitbrush (Chrysothamnus), snakeweed (Gutierrezia), groundsel (Senecio), and others Mustard family includes peppergrass (Lepidium), spectacle pod (Dimorphocarpa), watercress (Rorippa), tansy mustard (Descurainia), and others Cactus family includes nipple cactus (Mammillaria), hedgehog (Echinocereus), and others Pink family includes chickweed (Cerastium), sandwort (Arenaria), moss campion (Silene), and others Buckbrush Thistle Beeweed Squash Spurge family includes spurge (Euphorbia), noseburn (Tragia), copperleaf (Acalypha), and others Pea family includes locust (Robinia), locoweed (Astragalus), vetch (Vicia), sweetvetch (Hedysarum), and others Chicory tribe includes prickly lettuce (Lactuca), dandelion (Taraxacum), and others Lily family includes mariposa lily (Calochortus), onion (Allium), yucca (Yucca), beargrass (Nolina), and others Four o’clock family includes four o’clock (Mirabilis), spiderling (Boerhaavia), sand verbena (Abronia), and others Evening primrose family includes evening primrose (Oenothera), fireweed (Epilobium), beeblossom (Gaura), and others Cholla Prickly pear Grass family includes grama grass (Bouteloua), galleta (Pleuraphis), fescue (Festuca), dropseed (Sporobolus), and others Large grass includes reed (Phragmites), Indian ricegrass (Achnatherum), cereal grasses (e.g. wheat [Triticum], oats [Avena]), and others

Insect

Asteraceae

Brassicaceae

Cactaceae

Caryophyllaceae

Ceanothus Cirsium Cleome Cucurbita Euphorbiaceae

Fabaceae

Liguliflorae

Liliaceae

Nyctaginaceae

Onagraceae

Opuntia (Cylindro) Opuntia (Platy) Poaceae

Large Poaceae

Table 2 (continued ) Pollen taxa

Common name

Pollination mode

Polemoniaceae

Phlox family includes phlox (Phlox), linanthus (Leptosiphon), gilia (Gilia and Ipomopsis), and others Purslane Sumac and skunkbush/lemonade berry (Rhus trilobata and R. ovata) Rose family includes bitterbrush and cliffrose (Purshia spp.), mountain mahogany (Cercocarpus), blackbrush (Coleogyne), chokecherry (Prunus), and others Greasewood Penstemon family includes mullein (Verbascum), penstemon (Penstemon), Indian paintbrush (Castilleja), and others Buffaloberry Nightshade family includes tobacco (Nicotiana), wolfberry (Lycium), groundcherry (Physalis), and others Globemallow Meadow rue Cheno-Am includes saltbush and shadscale (Atriplex spp.), goosefoot (Chenopodium), pigweed (Amaranthus), winterfat (Krascheninnikovia), and others Fir Ragweed/bursage type Sagebrush Birch Mormon tea Buckwheat Walnut Juniper Spruce Pine Pinyon type Cottonwood/aspen type Oak Willow Tidestromia Cattail Maize

Insect

Portulaca Rhus Insect Rosaceae Insect

Sarcobatus Scrophulariaceae Insect

Insect

Insect Insect Insect Insect Insect

Shepherdia Solanaceae

Sphaeralcea Thalictrum Cheno-Am

Insect

Insect

Insect

Insect

Insect

Abies Ambrosia Artemisia Betula Ephedra Eriogonum Juglans Juniperus Picea Pinus Pinus edulis type Populus Quercus Salix Tidestromia Typha Zea mays

Insect Insect

Insect

Insect Insect

Insect Insect

Insect Insect Wind/ insect

Wind Wind Wind Wind Wind Wind Wind Wind Wind Wind Wind Wind Wind Wind Wind Wind Winda

a Though wind pollinated, the large and heavy grains of maize pollen seldom travel more than several meters from the plant (Jones and Newell, 1946).

Insect Insect Wind

Wind

entrained in sediment adhering to tool surfaces. To examine these issues, multiple pollen washes from 5 manos and 1 metate generated 13 samples for comparison (Table 4). Two paired sets of samples yielded significant counts: (1) a first wash from the artifact use surface targeting surficial sediments (the standard approach in pollen wash analysis) and a second, deeper wash from the same use surface (n ¼ 5 artifacts); and (2) use-surface and non-use surface washes from the same artifact (n ¼ 2). There is but one consistent pattern in the comparison of multiple washes: pollen concentration decreases from the first


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Table 3 Pollen washes from manos and metates recovered from prehistoric sites of various age excavated for the Navajo Mountain Road Archaeological Project Site

Chronology

Artifact contexts

Artifact washes (includes multiple washes from the same artifact) Manos

AZ-J-14-21

Pueblo III

Intramural

AZ-J-14-31 AZ-J-14-35 AZ-J-14-36 AZ-J-14-38 AZ-J-14-16 AZ-J-14-41 AZ-J-3-14

Basketmaker II Basketmaker II Basketmaker II Basketmaker II Pueblo II Early Archaic Pueblo II

Intramural Extramural Intramural Intramural Intramural Extramural Intramural

AZ-J-3-8 AZ-J-2-3

Basketmaker II Mid Pueblo III

AZ-J-2-6

Late Pueblo III

UT-B-63-30 UT-B-63-39 Total

Late Archaic Late Pueblo III 13 sites

Extramural Intramural and extramural Intramural and extramural Extramural Extramural

surface wash to the second, deeper wash (Table 4). This result suggests that there is a deeper embedded component of pollen beneath the surficial sediments. However, there is no significant difference in the composition or relative frequency of pollen types between the different surfaces. There is a weak relationship for enhanced representation of grass pollen in 4 of the 5 artifacts from the deeper use-surface washes, and in 3 of the 5 artifacts, sagebrush percentages were higher in the deeper wash, as compared to the first wash. This may in some way relate to cultural activities around the sites where the artifacts were used. It is also possible that there was more grass and sagebrush in the prehistoric landscape,

4

Metates

3

Controls

1

8

1

2 1

1 5 4

Sterile samples

1 1 1 3

3 2 2 1 2 1

controls, washes controls wash washes wash

2 3

1 control, 3 washes 1 wash

5 7

2 2

5

3

2 washes

1 6 30

1 wash 2 washes 6 controls, 15 washes

5 39

1 3 12

compared to post-occupation time, or there is some physical characteristic about sagebrush and grass pollen that adheres better to rock. 4.3. Control samples and pollen washes Seventeen artifacts from seven sites are represented by sets of one or more control samples and productive washes. We used this population of paired samples to explore whether there are unique assemblages from the washes that might relate to plant processing. Control samples were collected from the sediment in direct contact with the use-surface of

Fig. 1. Different sandstone textures for manos of the Navajo Mountain area: both are dense medium grain sandstone but (a) has abundant vesicles of various size, including large pits whereas (b) has sparse vesicles of small size.

P.R. Geib, S.J. Smith / Journal of Archaeological Science 35 (2008) 2085e2101 One-Hand Mano Two-Hand Mano Metate

15

10

5

8.0e+4 6.0e+4 4.0e+4 2.0e+4

9 8

0.0

7 6

8

5

dant6 vesic

abun

les

0 0

200

400

600

Artifact Surface Area

800

cm2

Fig. 2. Recovered sediment volume versus artifact surface area for 39 artifacts.

the artifact, from beneath the artifact, or from floor contexts containing the artifact, such as a structure or pit. Two patterns stand out in the comparisons (Table 5). Maize pollen is more common in the control samples; in the 15 sample pairs maize occurs in 7 control samples but just 2 washes. The second pattern is higher Cheno-Am percentages in wash samples than in controls: 10 of the 15 wash samples exceeded Cheno-Am frequencies in the controls. There was also a slightly higher occurrence of pollen aggregates in the control samples: 8 of the 15 washes recorded fewer pollen aggregates than corresponding control samples. The finding of maize pollen in control samples but few washes is explained by the results from our experimental studies (see below). Why Cheno-Am pollen is consistently higher on artifact surfaces than sediments in contact with or containing the artifact is unknown. Several plants comprise the broad Cheno-Am category (see Table 2) and all were used for a wide range of subsistence activities (Moerman, 1998). Deliberate use of Cheno-Am seeds throughout prehistory is well documented across the Southwest (e.g., Huckell

1.2e+5

Pollen Concentration gr/cc

1.0e+5

One-Hand Mano Two-Hand Mano Metate

1.0e+5

8.0e+4

6.0e+4

4.0e+4

2.0e+4

0 0

200

400

600

800

Artifact Surface Area cm2 Fig. 3. Pollen concentration (grains/cm3) by artifact surface area (cm2).

4

Vesic

4

2

ulari

spars

ty

e ves

0

icles

3

ze

Metate

Si

Two-Hand Mano 20

In co crea ar se sing n in ess

One-Hand Mano

Pollen Concentration gr/cc

Volume of Recovered Sediment cc

25

Gr a

2092

Fig. 4. Pollen concentration (grains/cm3) and rock texture.

and Toll, 2004; Hunter, 1999). In southeast Utah, Cheno-Am seeds were recovered in 46e71% of 155 coprolites recovered from Archaic layers in caves (Van Ness and Hansen, 1996). Cheno-Am was clearly an important food resource since early human occupation, and the enhanced representation from the artifact washes may reflect processing. However, the ChenoAm group contains many weed species that readily colonize disturbed ground, such as around sites, and especially in fields. Cheno-Am pollen is so ubiquitous from every type of Southwest archaeological context that some variable fraction of the pollen population, even on artifacts, must reflect ambient pollen from weedy and native taxa. 5. Experimental studies There is an obvious inferential gap between artifact pollen assemblages (the consequent) and human behavior (the antecedent), a gap that cannot be bridged by recourse to the archaeological record alone. To help establish inferential linkages we designed a series of experiments as an independent test of the assumption that pollen spectra recovered from grinding tool washes register the processed plants. Three basic research questions structured our experiments (see Table 1): (1) Can the pollen from a processed plant be traced through the various stages of processing: from raw or parched seeds through grinding on a metate? (2) Does ambient pollen swamp that of the target taxon while processing seeds in a field setting? (3) Does the domesticate architecture of maize ears lessen or eliminate a pollen signature on the consumed portions? Seeds from eight weeds and three grass species (Fig. 5; Table 6), plus the nuts of pinyon pine, were harvested and processed using a variety of traditional methods: winnowing, parching, and grinding to flour on a metate. The first phase of this study was conducted in a controlled laboratory setting to quantify how much pollen adheres to seeds through the various processing steps without the dilution effects of atmospheric pollen rain. Pollen remaining in the winnowed chaff was also quantified.


2093

Table 4 Summary results from multiple pollen washes from the same artifact Site no.

Pollen concentration (grains/cm3)

Artifact specimen

Use-surface 1st wash

Use-surface 2nd wash

AZ-J-2-3

Mano 800.09

26200

9700

AZ-J-2-3 AZ-J-2-3 AZ-J-2-6 AZ-J-2-6

Mano Mano Mano Mano

17200 24900 16800 31100

e 14600 11400 11500

AZ-J-3-14

Metate 689.01

30900

4100

620.03 620.04 832.01 950.02

Other (based on pollen percentages) Non-usesurface Grass and sagebrush highest in deep, second wash of use surface

e 14200 10000 e e

Sagebrush highest in deep, second wash of use surface Grass highest in deep, second wash of use surface Grass and sagebrush highest in deep, second wash of use surface Grass highest in deep, second wash of use surface

e

In a second phase of the study, the input of natural atmospheric pollen rain to assemblages was tested; seven of the seed taxa were ground outside on metates that had been exposed for several days, before and after grinding. Seed processing took place in two separate seasons (late summer and late fall) and in two separate environmental settings (forest and shrub grassland). We used these experimental findings to critically examine how an analyst might go about interpreting a series of pollen spectra obtained from prehistoric grinding tools. Note that the experimental metates were all of the same medium grain sandstone with sparse vesicles. A third set of experiments concerned maize, the staple grain of the North American Southwest after about 1000 BC. Considering that corn ears are tightly and completely encased in husks, there seemed little reason for maize pollen to be

present on kernels. Vorsila Bohrer (1972) found some maize pollen on kernels in an earlier study, but we were interested in exploring this result in greater detail. Specifically, to what extent the husk inherently restricts the addition of maize pollen to the kernels, such that there is no direct relationship between the food portion of maize and the representation of its pollen. We conducted a series of different washes to document the level of maize pollen that could be recovered from shucked kernels, husked ears, different layers of husks (exterior, middle, and interior), and maize silks. 5.1. Pollen through stages of seed processing In total, 83 pollen washes were completed from various stages of seed processing including grinding trials (Table 7);

Table 5 Pollen percentage data from artifact washes compared to controls Site

Artifact

Pollen wash vs. control (þ, higher %, , lower %)

Other

Pinyon

Juniper

Cheno-Am

Grass

Maize

Aggregates

AZ-J-14-21 AZ-J-3-8

Metate (669.05) Mano (685.04)

þ

þ

0 Control

0

AZ-J-3-8 AZ-J-14-16

Mano (730.01) Metate (624.04)

þ þ

þ

þ

þ

Same þ

Prickly pear in wash sample

AZ-J-14-16

Mano (660.71)

þ

þ

Wash Control and wash Control (same sample for both manos)

Beeweed and prickly pear in wash sample

AZ-J-14-16 AZ-J-2-3

Mano (660.72) Mano (800.09)a

þ þ

þ þ

þ þ

Wash

AZ-J-2-6

Mano (703.05)

0

þ

Control

AZ-J-2-6 AZ-J-3-14 UT-B-63-39

Mano (950.02)a Metate (689.01)a Mano (614.07)

þ þ

þ

þ þ þ

þ Same

0 Control 0

0

UT-B-63-39 UT-B-63-39 UT-B-63-39 UT-B-63-39

Mano (1145.01) Metate (1032.02) Mano (1282.02) Metate (682.02)

þ

þ þ þ

þ þ

0 0 Control 0

0 0 0

Sunflower family high in the wash, compared to the control

High beeweed (4%) in control; beeweed (1%) and cattail in wash sample High beeweed in control (21%) and wash (32%); high lily family in control (3%); prickly pear in control Beeweed and cholla in control Prickly pear in control Prickly pear and beeweed in control; cattail and parsley family in wash (trace in control) Beeweed in wash Beeweed in control Beeweed in control

þ, percentages from artifact wash exceeded control; , percentages from artifact wash less than the control; 0, no value from either the control or the wash sample. a Artifacts with multiple washes. The second, deep wash compared in this table.


2094

Fig. 5. Several of the seeds used in our experiment along with the resulting flour from grinding on a metate.

Table 6 List of plant seeds or nuts commonly exploited by native people of the American Southwest that comprised this pollen wash study Common name

Taxa

Pollen ecology

Seed characteristics

Ethnographic

Amaranth

Amaranthus albus

Wind-pollinated

Small

Amaranth Careless weed, amaranth

Amaranthus gracilis Amaranthus palmeri

Wind-pollinated Wind-pollinated

Goosefoot

Chenopodium leptophyllum

Wind-pollinated

Small Light, small, cylindrical, dry and tightly encased by spiny bracts. easy to winnow because fluffy chaff blows away Heavy and dry

Seeds winnowed and ground to flour; greens used for food (Castetter and Opler, 1936, pp. 16, 48); Navajo ground threshed seeds to flour (Vestal, 1952, p. 25) and used leaves in ceremonial tobacco (Elmore, 1944, p. 45) Same as above Seeds ground to meal (Castetter, 1935, p. 23; Elmore, 1944, p. 46); leaves cooked as greens (Curtin, 1949, p. 47)

Beeweed

Cleome serrulata

Insect-pollinated

Tansy mustard

Descurainia pinnata

Insect-pollinated

Sunflower

Helianthus annuus

Insect-pollinated

Heavy and oily; hulls ground with seed

Purslane

Portulaca spp.

Insect-pollinated

Indian ricegrass

Achnatherum hymenoides (Oryzopsis hymenoides)

Wind-pollinated

Tiny and light but easy to separate from chaff Heavy and dry, tightly encased in bracts that were ground along with seed

Dropseed grass

Sporobolus airoides

Wind-pollinated

Dropseed grass Corn

Sporobolus giganteus

Wind-pollinated

Zea mays

Wind-pollinated

Light and even after parching, hard to winnow and separate chaff Light but easier to separate from chaff than S. airoides Kernel

Pinyon pine

Pinus edulis

Wind-pollinated

Nut

Heavy and dry, easy to winnow Tiny, light, and oily. easy to winnow

Navajo used seeds for food (Vestal, 1952, p. 25). seeds one of the most important foods for Zuni (Castetter, 1935, p. 21); Zuni mixed ground seeds with corn meal, formed into balls and steamed (Stevenson, 1915, p. 66) Food staple, pottery paint (Adams et al., 2002) Navajo ground seeds to meal (Vestal, 1952, p. 28). Gila River Pima made pi~nole from ground seeds (Rea, 1997, pp. 223e224); widespread use of seeds and greens (Moerman, 1998, pp. 197e198) Seeds winnowed, parched, ground for food (Castetter and Bell, 1951, p. 187); widespread use of seeds and oil pressed from seeds for food and medicine (Moerman, 1998, pp. 257e258) Hopi used seeds for food (Elmore, 1944, p. 47); widespread use of greens for food (Moerman, 1998, p. 434) On the Colorado Plateau, seeds common from Archaic archaeological sites (Huckell and Toll, 2004, pp. 45, 48, 49). Hopi ground seeds with corn into fine meal (Nequatewa, 1943, p. 20). Navajo ground seeds into cakes (Elmore, 1944, p. 26) On the Colorado Plateau, seeds common from Archaic archaeological sites (Huckell and Toll, 2004, pp. 45, 48, 49) Hopi threshed seeds and ground with corn into fine meal for cooked mush (Nequatewa, 1943, p. 20) Food staple, important ceremonial plant (Moerman, 1998, pp. 610e612) Food staple (Moerman, 1998, p. 406e408)


2095

Table 7 Summary of 83 pollen washes by plant species and experimental treatment Common name

Taxa name

Specimen no.

Raw or winnowed seed

Chaff

Parched seed

Metates, laboratory grinding

Manos, laboratory grinding

Metates, field grinding

Amaranth Amaranth Careless weed, amaranth Goosefoot

Amaranthus albus Amaranthus gracilis Amaranthus palmeri

2A

e

3A, 3B

e

e

e

e e

1A, 1B

Beeweed Tansy mustard Tansy mustard

Chenopodium leptophyllum Cleome serrulata Descurainia pinnata Descurainia pinnata

e e

e e

e

e

Sunflower Sunflower

Helianthus annuus Helianthus annuus

e

e

e

e e

e

Purslane

Portulaca sp.

e

e

e

e

Grasses Indian ricegrass Indian ricegrass Indian ricegrass

Achnatherum hymenoides Achnatherum hymenoides Achnatherum hymenoides

e

e e e

e a

e

e

e e

Indian ricegrass

Achnatherum hymenoides

e

e

e

e

e

Dropseed grass Dropseed grass Corn

Sporobolus airoides Sporobolus giganteus Zea mays

b

c

e

e

e

e e

Pinyon nuts Pinyon pine

Pinus edulis

d

e

e

e

e

e

28

18

12

9

9

7

4A, 4B Highway 89, Flagstaff 8B Long House Valley

5A field burned 9B not field burned Blue Canyon, raw seed, not field burned, not winnowed Blue Canyon, field burned, not winnowed 6A, 6B 7A, 7B 9 specimens

Totals a b c d

Seed winnowed after parching. Nine of kernels, 5 of ears. Twelve of husks and silks. Raw nuts in the shell.

76 of these washes were from processing stages and grinding trials conducted in a controlled laboratory setting to exclude ambient pollen. If the data are evaluated by pollen concentrations, one general trend across all seed washes was for the pollen from the processed taxon (target) to exceed the combined values of other (non-target) pollen types (Table 8; note that this excludes pinyon pine since the wash of raw nuts did not yield any pollen). Even so, there are three partial exceptions: (1) amaranth pollen was approximately equal to other pollen types from raw (winnowed) seed, parched seed, and laboratory grinding on a metate; (2) beeweed pollen was less than other types from raw and parched seed; and (3) the concentration of Indian ricegrass pollen was less than other types for parched seeds. Even in these cases, a palynologist would recognize the processed seed because there are several taxa combined in the other category and the amaranth, beeweed, and ricegrass values are higher than any individual type. That the target taxon exceeded the combined values of other pollen types might be expected in this case given the care taken to limit ambient pollen. We did this purposefully to represent a ‘‘best case’’ scenario where the signature of the target taxon would be least ambiguous, something that is not always true (see Adams, 1988).

Another finding of our experimental washes was the variability in pollen concentration between species. Tansy mustard, sunflower, and Cheno-Am produced more pollen than amaranth and beeweed at each step of the process. The decline in abundance from raw seed to metate wash was also variable between taxa. For example, there was 68 times more amaranth pollen in the raw seed than in the metate wash, and for tansy mustard there was 22 times more mustard pollen in the raw seed compared to the metate. Of the two species of dropseed grass collected, the raw seed of Sporobolus airoides yielded 65 times more pollen than the lab metate wash, but the raw seed from S. giganteus yielded only nine times more pollen. There were also differences in the distribution of pollen aggregates between taxa. Target taxon pollen aggregates were absent from some plants (beeweed and amaranth) at all stages of processing, but common in other species (tansy mustard and grasses); for two species (beeweed and sunflower) a few aggregates occurred in the metate washes but not in parched seed. An important general trend of our experimental washes is the documented decrease in pollen abundance through each step of seed processing, with the largest decrease for all plants

2096


Table 8 Pollen concentrations and percentages for seed and metate washes Taxon

Specimen

Preparation

Goosefoot (Chenopodium leptophyllum)

Chle 1A Chle 1B Chle 1B Chle 1B Ampa 3A Ampa 3B Ampa 3B Ampa 3B Depi 4A Depi 4B Depi 4B Depi Hwy89 Hean LHV Hean 8B Hean 8B Hean LHV Clse Clse Clse Spai 6A Spai 6B Spai 6B Spgi 7A Spgi 7B Spgi 7B Spgi 7B Achy Blue Canyon

Winnowed Parched seed Lab metate Field metate Winnowed Parched Lab metate Field metate Winnowed Parched seed Lab metate Field metate Winnowed Parched seed Lab metate Field metate Raw seed Parched seed Field metate Winnowed Parched seed Lab metate Winnowed Parched seed Lab metate Field metate Raw seed, not winnowed Parched seed Field metate Parched/ winnowed Lab metate

Amaranth (Amaranthus palmeri)

Tansy mustard (Descurainia pinnata)

Sunflower (Helianthus annuus)

Beeweed (Cleome serrulata) Dropseed grass (Sporobolus airoides Spai) (Sporobolus giganteus Spgi)

Indian ricegrass (Achnatherum hymenoides) not field burned

Achy Blue Canyon Achy Blue Canyon Achy 9B Achy 9B

Concentration grains/g (rounded to nearest 10 grains)

Pollen percentages

Pollen aggregates of target taxon no. (largest size)

Target

Other

Target

Other

19330 4750 1090 1500 13560 2490 200 160 21210 9840 980 190 528950 6720 4880 620 140 60 30 286420 56380 4400 44900 36490 5020 70 8490

2790 620 160 560 17980 2090 270 680 4820 1640 410 150 7270 690 2990 340 320 230 550 4560 520 3490 4490 3210 430 1890 6810

87 89 87 63 43 54 42 19 81 86 71 57 98 91 62 65 30 20 5 98 99 56 91 92 92 4 55

13 12 13 37 57 46 58 81 19 14 29 43 1 9 38 36 70 80 95 2 1 44 9 8 8 96 45

e e 3 (8) 1 (6) e e e e 2 (50) 2 (8) 2 (6) 2 (6) Scan (36) e 1 (3) e e e e Scan (50) 3 (16) 2 (4) Scan (12) 1 (7) 5 (10) e e

160 20 190

290 90 60

36 19 76

64 81 24

1 (6) e 1 (3)

380

360

51

49

6 (7)

‘‘target’’ refers to the pollen taxon expected for the seed processed, ‘‘other’’ refers to non-target pollen taxa (pinyon is not reported here because a wash of raw nuts yielded no pollen).

occurring between the washes of raw (winnowed) seed and parched seed. Pollen percentages generally track the same trends as pollen concentrations (Table 8), but the smoothing effect mutes the magnitude of the variability between raw and parched seed washes in individual species. Where does the pollen go in its decline from raw to parched seeds? The answer is that the pollen remains on the chaff, and the amount is variable by species. Washes of winnowed chaff from six seed taxa produced consistently higher pollen abundance than washes of the parched seed, or in the case of purslane, winnowed seed (Table 9). The difference in abundance is exponential in goosefoot, amaranth (Amaranthus gracilis), sunflower, and Indian ricegrass, and not quite as dramatic in the beeweed and purslane. The findings from the chaff washes have important implications for archaeological pollen sampling. Places where harvests were stockpiled, leaf-stripped, and parcheddwhere the chaff accumulateddwould provide one of the best contexts for archaeological pollen samples. How archaeologists might go about recognizing such places

at open prehistoric sites is no easy matter and would probably vary temporally, spatially, and culturally. The chaff washing experiments explain some of the variability in concentrations between taxa because seeds that are difficult to separate from chaff would leave more pollen on grinding tools than clean seeds. For example, the large and heavy seeds of beeweed are easily separated from the chaff, which consists of light-weight pods; even while simply collecting this seed, much of the chaff can be eliminated. In contrast to this is goosefoot, which has seeds tightly sheathed in leaf-like cases that are not easily eliminated. There is also great variety in seed packaging. Beeweed seeds develop within an enveloping pea-like pod that greatly reduces the chances of pollen adhering to the actual seed coats. Beeweed pollen does not occur in any abundance on seeds or even the chaff, registering well below other pollen types in concentration and percentage (see Tables 8 and 9). This is not true however for goosefoot, a wind-pollinated plant, where the target taxon represents just under 90% of observed pollen.


2097

Table 9 Comparison of pollen results from chaff and seed (parched or raw) Taxon

Goosefoot (Chenopodium leptophyllum) Amaranth (Amaranthus gracilis) Sunflower (Helianthus annuus) Beeweed (Cleome serrulata) Indian ricegrass (Achnatherum hymenoides) Purslane (Portulaca sp.)

a

Preparation

Chaff Parched seed Chaff Parched seed Chaff Parched seed Chaff Parched seed Chaff Parched seed Chaff Winnowed raw seed

Concentration grains/ga

Pollen percentages

Target

Other

Target

Other

Pollen aggregates of target taxon no. (largest size)

54130 4750 147910 930 92270 1350 2780 60 12180 160 4390