A systematic approach to species–level identification of chile pepper (Capsicum spp.) seeds:...

A Systematic Approach to Species–Level Identification of ChilePepper (Capsicum spp.) Seeds: Establishing the Groundworkfor Tracking the Domestication and Movement of Chile Peppersthrough the Americas and Beyond1

KATHERINE L. CHIOU* AND CHRISTINE A. HASTORF

Department of Anthropology, University of California, Berkeley, CA, USA*Corresponding author; e-mail: [email protected]

A Systematic Approach to Species–Level Identification of Chile Pepper (Capsicum spp.) Seeds:Establishing the Groundwork for Tracking the Domestication and Movement of Chile Peppersthrough the Americas and Beyond The chile pepper (Capsicum spp.), a plant held in great esteemthroughout history, was independently domesticated in a series of places including highlandBolivia, central Mexico, the Amazon, the Caribbean, and other locales with a particularly longhistory of cultivation and use in the central Andes of South America. Though identification of chilepepper species through fruit morphology is possible and has been utilized by botanists studyingmodern and archaeological specimens, species–level identification of Capsicum seeds hasremained undetermined. Given the greater abundance of seed remains in the archaeologicalrecord due to the higher likelihood of preservation, the ability to identify specific Capsicumdomesticates has profound implications for tracking the domestication and spread of chilepeppers prehistorically through the Americas and historically through trade and exchange tothe rest of the world. This article presents a systematic procedure to identify Capsicum seeds tothe species level created by adopting a morphometric approach to compare attributes of modernCapsicum seeds to archaeological seeds.

Un Procedimiento Sistemático para la Identificación de Diversas Especies Chiles/Ajíes(Capsicum spp.) por medio de Sus Semillas: Estableciendo una Base para Rastrear laDomesticación y Movimiento de los Chiles/Ajíes a través de las Américas y el Resto delMundo El chile/ají (Capsicum spp. L.), una planta que goza de gran estima a lo largo de lahistoria de la humanidad, fue domesticado independientemente en una serie de diferenteslugares, incluyendo el altiplano boliviano, México central, la Amazonia y el Caribe. Aunque hoyen día es possible la identificación de diferentes especies de chile/ají a través de lamorfología de lafruta, la identificación utilizando solamente la semilla permanece una tarea difícil. Dada la granabundancia de semillas en el registro arqueológico, el desarollo de esta habilidad tiene profundasimplicaciones para el estudio de la domesticación y difusión de chile/ají en las Americaprecolombina y el resto del mundo. El presente artículo propone un procedimiento sistemático

1 Received 7 November 2013; accepted 14 August2014; published online 16 September 2014.

Electronic supplementary material The online versionof this article (doi:10.1007/s12231-014-9279-2) containssupplementary material, which is available to authorizedusers.

Economic Botany, 68(3), 2014 pp. 316–336© 2014, by The New York Botanical Garden Press, Bronx, NY 10458-5126 U.S.A.

para identificar especies de Capsicum adoptando un acercamiento morfométrico para comparerlas semillas modernas con restos arqueológicos.

Key Words: Archaeobotany, Capsicum, Chile peppers, Seed identification, Seed morphology,Ethnobotany.

An Introduction to the Genus Capsicum

Chile peppers, a staple of many cuisinesaround the world today, have their origins inthe Western Hemisphere. Prior to the 15th cen-tury, chile peppers were cultivated to varyingextents from Chile to the American Southwest(Fig. 1). The chile pepper (Capsicum spp.) consistsof about 25 species, five of which represent domes-ticated taxa (Andrews 1984; Basu and De 2003;Davenport 1970; Eshbaugh 1976, 1980; Eshbaughet al. 1983; Heiser 1971; Heiser and Smith 1953;Naj 1992; Perry 2012). These taxa includeC. annuum L., C. baccatum L. var. pendulum(Willd.) Eshbaugh, C. chinense Jacq., C. frutescensL., and C. pubescens Ruiz & Pavon. The generalconsensus among botanists is that the nuclear originarea for the Capsicum genus is in highland Boliviaon the eastern slopes, which is also the purportedorigin of the domesticated C. pubescens. From there,the wildCapsicum species radiated outward throughthe pre–Holocene Americas due to dispersal bybirds and only much later by humans (Andrews1984, 2006; Eshbaugh et al. 1983; Pickersgill1977, 1988, 2009). The evidence suggests thatthere was a range of wild Capsicum species through-out Central and South America by the time peoplearrived in the area. C. baccatum is thought to havebeen domesticated in lowland Bolivia or coastalPeru, while C. chinense and C. frutescens may havemore tropical roots in the northeastern Amazon(Aguilar–Meléndez 2006; Aguilar–Meléndez et al.2009; Eshbaugh 2012; Hernández–Verdugo et al.1999, 2001; Moses and Umaharan 2012; Perry andK. Flannery 2007; Pickersgill 1972).C. annuum, onthe other hand, was domesticated in Mexico(Aguilar–Meléndez 2006; Kraft et al. 2014;Pickersgill 1972). While botanists have painted apicture of Capsicum domestication based on themodern distribution of wild Capsicum taxa in theAmericas as well as the presence of preservedCapsicum fruits with calyx morphology intact fromarchaeological sites, the lack of certainty surround-ing the identification of Capsicum seeds to species–level has hindered this effort of tracing Capsicumspecies domestication and their movements, withsome proclaiming Capsicum seed identification to

the spec ies leve l imposs ib le and othersmisidentifying seeds as the incorrect species(Andrews 1984; Pickersgill 1969; Towle 1961).Based on the research presented here, we argue theopposite. We believe that the analysis of both quan-titative and qualitative traits of archaeologicalCapsicum seeds can indeed lead to species–levelidentification. Analyses conducted on modern andearlyCapsicum starches, for example, have suggestedthat Capsicum (in particular, C. baccatum,C. frutescens, and C. pubescens) starch grains havespecies–diagnostic morphotypes (Perry and K.Flannery 2007). In this article, we present the re-sults of our morphometric attribute analysis of seedsof domesticated members of the genus Capsicum,which we believe will prove useful to scholars en-gaged in Capsicum research. We (1) recorded datafor 27 qualitative and quantitative attributes ofmodern C. annuum, C. baccatum, C. chinense,C. frutescens, and C. pubescens, (2) determinedwhich eight qualitative and quantitative attributesprovided the greatest utility in Capsicum seed iden-tification, and (3) developed a seed identificationguide for chile peppers. Our research will aid in thestudy of the unique histories of various Capsicumdomesticates that are reflected in seed morphology(Chiou and Hastorf 2012; Chiou et al. 2014).

BACKGROUND ON CAPSICUM RESEARCH

Capsicum spp. was first encountered by theEuropean explorers in the late 15th century duringa quest for expanding the spice trade by Columbusand his men on the West Indian island ofHispaniola. There, they encountered a plant thatthe native Arawak Indians called axí/ají. Like manyof the explorers of the era, they were in search of aroute to the spices of Asia, and in particular, blackpepper (Piper nigrum L.). Upon encountering ají,the Spanish named it pimiento (pepper) as its flavorand spiciness reminded them of the Asian pepper.The chile portion of the common name derivesfrom Nahuatl (chīlli). Across the Americas, thereare many names for the chile pepper such as uchuin Quechua or huayca in Aymara. As with many ofour continental plants, the Nahuatl or Caribbeanwords have dominated (Andrews 1984).

317CHIOU & HASTORF: CAPSICUM SPP. SEED IDENTIFICATION2014]

Chile peppers have long held a position of greatesteem in the New World. Indeed, chile pepperswere used in pre–Columbian times as an essentialingredient in the preparation of dishes (such as theAztec chocolatl, a concoction made from groundcacao beans and flavored with vanilla and chile),serving as what one might call a “signature food”(Gasser and Kwiatkowski 1991; McNeil 2006;Perry 2012). Much like rice among the Japanese,

the chile pepper had close ties to notions of identityand self in the Americas (Ohnuki–Tierney 1993).In the Andes of South America, we know thatcertain cultivars of chile pepper are restricted tospecific regions (i.e., highland, coast, and jungle),suggesting the possibility that different groups ofpeople identified with these distinct species andused the different species for different dishes.Among the Nasca, for example, chile peppers are

Fig. 1. Distribution of Capsicum species at European contact ca. AD 1530 (redrawn from Andrews 1984; Heiser1976; McLeod et al. 1982).

318 ECONOMIC BOTANY [VOL 68

the second most depicted plant in Nasca ceramiciconography, commonly shown attached to mythi-cal beings (Proulx 2009).

Early Evidence for Chile Pepper in the Americas

In terms of early chile pepper evidence,Capsicum seeds have purportedly been found indeposits dating to as far back as 10,000 B.P. atGuitarrero Cave located in modern–day Peru,though this date is disputed since Phaseolus remainsfrom the site have been directly dated to around3000–4000 B.P. (Kaplan and Lynch 1999; Pearsall2008). Starch grains of Capsicum have also beenrecovered dating back to 6000 B.P. from RealAlto and Loma Alta in Ecuador (Perry and K.Flannery 2007). Indirectly dated Capsicum seedsfrom early deposits at Puebla in the TehuacánValley and Tamaulipas (Ocampo caves) of Mexicosuggested a date of 9000–7000 B.P., though subse-quent AMS dating of maize remains fromTehuacánhave yielded a more recent age at 5600 cal. B.P.(Kraft et al. 2014; Long et al. 1989; Mangelsdorfet al. 1965; McClung de Tapia 1992; Smith 1967,1987). Similarly, AMS dating of bottle gourd andsquash from Ocampo have been dated to 6400–6000 cal. B.P. (Kraft et al. 2014; Smith 1997).Overall, the literature claims that the chile pepperwas cultivated by at least 7000–9000 B.P. (Chiouand Hastorf 2012; Kraft et al. 2014; Perry 2012;Pickersgill 1969). Recent research at the sites ofHuaca Prieta and Paredones have pushed this dateback further, with a directly dated Capsicum seedfrom the pre–mound occupational levels atParedones radiocarbon–dated to 9330 +/– 40 cal.B.P. (Beta–343109: 10,430–10,650 cal. B.P.,Chiou et al. 2014).

Local and Global Perspectives on Capsicumthrough Space and Time

The domestication of the Capsicum genus and itsvarious species has been the subject of a fair amountof botanical work that has greatly informed our ownresearch. According to Barbara Pickersgill, domesti-cated species ofCapsicum are somewhat distinct anddifficult to cross, producing sterile hybrids evenwhen fertilization is successful, though this appliesless so to the “annuum” complex that includesC. annuum, C. chinense, and C. frutescens(Pickersgill 1972; Eshbaugh 2012). Thus, cultivat-ed species of Capsicum had distinct wild ancestors

and were characteristic of different areas in pre–Conquest times (Smith and Heiser 1957). Giventhese traits, the Capsicum genus serves as a potentialproxy for studying human interactions in theAmericas, as “[g] enera in which several species havebeen domesticated may thus be useful indicators ofcultural contact if the place of domestication of theindividual species is accurately known and if thearchaeological material can be assigned with certain-ty to a particular species or group” (Pickersgill1972:99). Aguilar–Meléndez and colleagues’ genet-ic work (2009) has revealed that there are four majorsubspecies of C. annuum in Mexico, with the one inthe Yucatan Peninsula being spatially discrete today;in the west and north, the other three overlap.These sub–species variants aid us in visualizingearlier local engagement with the wild species aswell as the fluidity of the three sub–species in ex-change and sharing. From ethnographic, ethnohis-toric, and archaeological evidence, we know thatchile peppers have been used in specific recipes forat least 5,000 years. Nevertheless, most of thesevarieties are quite localized, suggesting quite a strongbelief in the quality of one’s local variety (Aguilar–Meléndez 2006; Hastorf 1998; Hugh–Jones 2001).

Given that the presence or absence of differentCapsicum species can reveal valuable informationabout cultural contacts, the ability to identifyCapsicum plant parts, especially seeds given theircommon presence in the archaeological record, iscrucial. The identification of Capsicum seeds in thearchaeological record up to this point has remainedsomewhat unsystematic. Margaret Towle, for exam-ple, reported that the majority of Capsicum remainsreported from coastal, pre–Columbian Peru wereC. annuum, which presents an unlikely scenariogiven that there are at least two species ofCapsicum (C. baccatum and C. chinense) that arenative to the central and western Andes (Towle1961). Subsequent research has suggested thatC. annuum was relatively restricted to Mexico andCentral America in the pre–Colombian times. Eventhough wild progenitors to C. annuum exist fromMexico to Colombia, genetic studies have shownthat the most parsimonious scenario for C. annuumdomestication is in Mexico, since all C. annuumplants have two pairs of acromere chromosomes,while most wild taxa have one except for wildspecies in Mexico (Aguilar–Meléndez 2006;Pickersgill 1972). Furthermore, at Huaca Prieta,previous work on Capsicum has revealed the pres-ence of C. baccatum or C. chinense by the LatePreceramic (Pickersgill 1969). Pickersgill identified


Capsicum pod remains housed in Margaret Towle’scollection at the Harvard Botanical Museum thatwere recovered from Junius Bird’s excavations in1947–1948 (Bird 1985). These identifications weremade based on calyx morphology (Pickersgill1969). While most of her discussion centered onchile pepper pods, Pickersgill reported the range ofdiameters for the seeds that were also recovered.While these data may be useful for arriving at ageneral sense of seed size, they do not lend verymuch insight to species–level identification. Afterour review of the literature, we determined that thebest course of action would be to complete atargeted study on seeds of all the domesticated chilepepper species to learn if they have the potential tobe uniquely identifiable.

Project Overview and Goals

This project was conceived after chile pepperseeds identified as Capsicum spp. from thePreceramic archaeological sites of Huaca Prietaand Paredones in the Chicama Valley of the desertNorth Coast of Peru and recovered through flota-tion of sediment samples during excavations led byTom Dillehay of Vanderbilt University and DuccioBonavia of the Academia Nacional de la Historiawere sent to the McCown ArchaeobotanyLaboratory at the University of California,Berkeley for analysis. In attempting to analyze thisrich data set spanning 4,000 years, which included avast number of Capsicum seeds that appeared todisplay some variation, we realized that a systematicanalysis of Capsicum seeds was essential to under-stand what was occurring at this site, which hassome of the earliest evidence of agriculture inSouth America. Given the sparse nature of theliterature on Capsicum seed identification (withsome notable exceptions, such as Gunn andGaffney 1974, which includes descriptionsconcerning seed coat, general seed dimensions,and the embryo of C. frutescens and C. annuum,Martin (1946), which includes drawing anddescription of the curved, linear C. baccatumembryo in comparison with other members of theSolanaceae family, and Minnis andWhalen (2010),which includes description of the first cultivatedC. annuum chile pepper seed found in northwestMexico/the American Southwest), we decided torecord both qualitative and quantitative attributesof modern seeds we obtained from various sourceslisted in Appendix 1 (Electronic Supplementary

Material, ESM), drawing inspiration from MariaBruno, Christine Hastorf, and BrieAnna Langlie’sprevious work on Andean Chenopodium (Bruno2006; Bruno and Whitehead 2003; Langlie et al.2011). Our goal was to determine diagnostic traitsof modern Capsicum seeds that could be applied toour archaeological analysis, the results of which arepresented elsewhere (see Chiou et al. 2014).

Methods for Modern Capsicum SeedIdentification

Studying a comparative collection of modernCapsicum seeds from all five domesticated specieswas crucial to the goals of this project, allowing us todetermine diagnostic attributes fromwell–identifiedseeds that could be used to identify archaeologicalseeds. To that end, we amassed 44 distinct seedcollections representing several examples of each ofthe domestic species—C. annuum, C. baccatum,C. chinense, C. frutescens, and C. pubescens—fromdifferent sources including vendors specializing inchile pepper cultivation and the USDA NationalPlant Germplasm System/Germplasm ResourcesInformation Network (Appendix 1, ESM). Theseseeds were photographed using an Olympus SZ–61stereomicroscope (10x–30x) and an Olympus digi-tal camera (model DP72) housed in the McCownArchaeobotany Laboratory. Close–up scanningelectron microscopy (SEM) images of the testa weretaken using a Hitachi TM–1000 located in theRobert D. Ogg Electron Microscopy Laboratoryon the UC Berkeley campus. The OlympusMicroSuite program was used to take various mea-surements of the whole seed, the attachment scar,and the testa in the transverse cross–section.Qualitative assessments were also made of the seedshape and testa texture.Initially, we identified and recorded 27 attributes

for each of the 44 Capsicum seed collections that arelisted and defined in Fig. 2. These attributes wereselected based on the limited Capsicum literature(e.g., length and width measurements inPickersgill 1969; Gunn and Gaffney 1974), previ-ous research experience with seed morphology, andobservations that were made concerning the natureof Capsicum seeds themselves (i.e., variation in“beak” length relative to the seed body, varying testathickness at seed margins, and differences regardingthe attachment scar).


Analysis

After we recordedmeasurements for 27 attributesfor each modern Capsicum seed species and variety,we ran a series of exploratory data analyses to seekthe most productive differentiating measurementsfor seed identification, such as plotting two attri-butes against each other (x by y) and generatingscatter plot matrices with multiple variables. Fromthese plots, we determined that six quantitativeattributes combined to form diagnostic identifica-tions of Capsicum seeds to species–level. Combinedwith our qualitative attributes, we now have eightdiagnostic characteristics. The two qualitative/nominal attributes are seed shape and testa texture.Our six quantitative attributes are (1) the ratio ofmaximum seed length to perpendicular width, (2)beak angle, (3) beak prominence, (4) whole seedsphericity, (5) the ratio of the thickest portion of thetesta to the thinnest portion, and (6) attachment

scar sphericity. These eight diagnostic attributes aredefined below.

DEFINITIONS

Seed Shape

The general shape of Capsicum seeds is relativelydistinct from species to species with some overlap.The range of seed shapes are drawn in Fig. 3 witharchaeological correlations from Huaca Prieta andParedones included.

Testa Texture

Testa texture refers to the appearance of the seedcoat (Fig. 4). Reticulation is defined by a 3–Dnetted pattern on the seed surface smooth to broadreticulation (A) refers to small curved undulations oftroughs and ridges in the testa surface. Tight

Fig. 2. Definitions of seed attributes analyzed in this study. Starred attributes are diagnostic.


reticulation (B) refers tightly concentrated ridgesand dramatic (C) refers to very large and pro-nounced ridges, particularly at the outer margins.The texture of the seed coat is diagnostic espe-

cially in the case of C. pubescens, which displays anexaggerated reticulation pattern on the outer mar-gins of the seed as well as does C. baccatum, whichexhibits a tighter reticulation pattern (as opposed tothe other species that tend to have a smoothsurface).

Maximum Length: Perpendicular Width

The length and width measurements are illustrat-ed in Fig. 5. The length measurement was takenfrom the beak and the width measurement wastaken perpendicular to the length measurement.All seeds were measured in the same manner (seeFig. 5A). This measurement was more diagnosticthan measuring without the beak (placing the seed

in an upright position and measuring on verticaland horizontal axes).

Beak Angle

The beak is defined as the protruding area of theseed that differentiates Capsicum seeds from othersimilar–looking seeds of the family Solanaceae(Gunn and Gaffney 1974; Minnis and Whalen2010). Figure 5 illustrates the morphometrics takenwith the whole seed and depicts how beak angle wasmeasured. The beak angle (Fig. 5B) gives us a senseof how much the beak diverges from the rest of thebody. A high beak angle, for example, is one of thediagnostic attributes for C. frutescens seeds.

Beak Prominence

Beak prominence is depicted in Fig. 6 and refersto the extent to which the beak protrudes from the

Fig. 3. Capsicum seed shape categories (including body and attachment morphology) based on modern andarchaeological seed data.


Fig. 4. Testa texture categories of the five Capsicum domesticates: A) smooth to broad reticulation B) tightreticulation and C) dramatic reticulation.


rest of the seed body and is an ordinal scale based ona rank: 1 refers to no protrusion and 5 is consideredprominently protruding.

Whole Seed Sphericity

Sphericity refers to how spherical (or in the two–dimensional sense, circular) a shape is and wascalculated using the Olympus MicroSuite program.Photos such as those in Fig. 7 show examples of fivemodern taxa with several morphometrics. Note thesphericity measurement and the general shape of theseed associated with each one.

Ratio of Thick Testa to Thin Testa

We made a transverse cross–section cut ofeach seed to measure testa thickness, often animportant measurement in studying domestica-tion, as testas tend to get thinner as a result of

directed selection pressure during domestication(Bruno 2006; Bruno and Whitehead 2003;Flannery 1973; Fritz and Smith 1988; Smith2006). Noticing a great amount of variation in themeasurements of the testa (especially at the outermargins), we decided to calculate a ratio of the thicktesta to the thin testa and trace that measurement.Three measurements are taken for each of the thickand thin testa areas, averaged and compared in aratio (Fig. 8). We found this to be a useful mea-surement, as there is a range of these ratio values.C. annuum has a small thick to thin testa ratio(3.44) whereas C. pubescens displays the greatestthick to thin testa ratio (5.92).

Attachment Scar Sphericity

The attachment scar or hilum refers to the areathat is attached to the placental wall of the chilepepper fruit. We noticed that the shape of the

Fig. 5. Seedmorphometrics including (A) maximum length (measured from the beak): perpendicular width and (B)beak angle (measured from vertical beak edge).

Fig. 6. Beak prominence ranking scale (from no beak [1] to extremely prominent vertical beak [5]).


attachment scar varied and decided to measuresphericity of the attachment scar shape (Fig. 9).

PLOTTING THE DISCRETE DIAGNOSTIC

ATTRIBUTES

Discriminant analysis is useful in investigatingdifferences among multiple groups, indicatingwhich variables contribute most to group separationand is often used in ecological, biological, paleonto-logical, and archaeobotanical analyses involvingmorphometrics (Hammer and Harper 2006;

Pearsall et al. 1995; Strauss 2010; Zhao et al.1998). It is appropriate for datasets with continuousoutcome variables and a priori established groupsthat are based on extrinsic criteria and when applied,classifies objects into groups by analyzing the rela-tionships between variables of the objects and theboundaries defined in terms of these variables. Inour study, we conducted linear discriminant analy-sis (LDA) on the modern Capsicum seed data setusing our six diagnostic, quantitative attributes inJMP 7 (JMP. Version 7 1989, Perry et al. 2007). InFig. 10, it appears that all five species separate

Fig. 7. Comparative examples of morphometric data for the five domesticated Capsicum taxa.

Fig. 8. Transverse cross–section morphometrics of the testa. Three measurements were taken of the thin and thickportions of the seed margin and averaged. A ratio was generated consisting of thick testa average: thin testa average.


completely. The two canonical axes explain 96% ofthe variance, and the circles in the figure represent95% confidence intervals on group centroid means.The lines radiating outwards are the correlationcoefficients between the first two axes and each ofthe six variables. For instance, the line representingthe variable Beak Angle shows that this variable ispositively correlated with the first canonical axis.Overall, the model does an excellent job of

achieving classification. It must be noted, however,that low sample counts in some of the groups affectt h e d i s c r im in an t a n a l y s i s , u l t ima t e l yoveremphasizing group differences. We expect tosee increasing overlap among the groups as wecollect more modern seed data. Nevertheless, thediscriminant functions only misclassified one seedor 2.22% of the sample (Table 1, Table 2). It isinteresting to note that, save for one seed (a

Fig. 9. Attachment scar morphometrics: (A) attachment scar width: attachment scar length and (B) attach-ment scar area.

Fig. 10. Discriminant analysis of seeds from the five domesticated Capsicum taxa with six quantitative diagnosticattributes.


C. annuum in the C. chinense group), C. chinense,C. annuum, andC. frutescens are somewhat separate.This trio is closely related geographically and genet-ically, forming the “annuum complex,” one of thethreeCapsicum groups with the other groups namedthe “baccatum complex” and the “pubescens com-plex” (Eshbaugh et al. 1983; Eshbaugh 2012;Jensen et al. 1979; McLeod et al. 1979; Stommeland Albrecht 2012). Sexual crosses are possibleamong species within a complex with varying de-grees of difficulty. The taxonomy of the “annuumcomplex” is a subject of debate, with some opposi-tion to the splitting of C. annuum, C. chinense, andC. frutescens into three distinct species (Eshbaugh2012). It is worth noting that the “pubescens com-plex” is the most isolated of the three groups(Stommel and Albrecht 2012). Our data suggestthat despite this close relationship, morphologicaldistinctions still exist. From our study of the fivemodern domestic Capsicum taxa, we believe thatmeasuring the six attributes we have chosen is suf-ficient to identify both modern and archaeologicalwhole domestic Capsicum seeds.

Discussion

Our morphometric attributes revolve aroundmeasurements of the whole seed, the attach-ment scar, and the testa in cross–section.Measurements of the whole seed include thatof the traditional length and width measure-ments and beak angle, along with other mea-surements easily calculated by Microsuite anddefined in Table 3 (see Fig. 5 for length, width,and beak angle measurements). Figure 9A and B

exhibit the attachment scar measurements we re-corded that included length, width, and area (as wellas sphericity of the attachment scar shape). Themeasurements taken on the transverse cross sectionof each Capsicum seed is illustrated in Fig. 5, whileFig. 6 illustrates the ranking scale we used to rankbeak protrusion. All 27 attributes were recorded forthe 44 modern seeds in our study sample. Figure 7exhibits a selection of five seeds, one from eachmodern taxon with their beak angle, maximumlength: perpendicular width, beak prominence,and whole seed sphericity data noted for a sense ofthe variation among species in regards to the seed in itsentirety. As is evident in Fig. 7, C. baccatum displaysthe most prominent beak, with C. pubescens gener-ally lacking or having very little beak protrusion.Furthermore, C. chinense tends to be the mostcircular in shape, which explains its higher spheric-ity value. Furthermore, while the beak ofC. baccatum tends to protrude straight up on theright side of the side at an angle of near 0°,C. chinense, C. frutescens, and C. annuum havemuch higher beak angles. Figure 11 shows thevariation in attachment scar shape among the fivedifferent Capsicum seeds as well as their sphericity.On average, C. baccatum tends to have the mostlinear–shaped attachment scar with a sphericity of<0.03. C. chinense, on the other hand, generallyexhibits a more circular attachment scar shape withsphericity as high as 0.33. Figure 12 presents draw-ings of the margins of the seeds in the transversecross–section. While C. annuum appears to havethin margins all–around its cross section,C. pubescens has the greatest ratio of thick tothin testa ratio. Using these discrete attri-butes, we have created a general guide to

TABLE 1. EIGENVALUES OFCANONICAL AXES.

Eigenvalue Percent Cumulative percent Canonical correlation

9.92980329 73.7292 73.7292 0.953156363.01528713 22.3886 96.1178 0.866574760.48254802 3.5829 99.7007 0.570513450.04030466 0.2993 100.0000 0.19683275

TABLE 2. COUNTS: ACTUALROWS BY PREDICTED COLUMNS.

Annuum Baccatum Chinense Frutescens Pubescens

Annuum 18 0 1 0 0Baccatum 0 12 0 0 0Chinense 0 0 4 0 0Frutescens 0 0 0 5 0Pubescens 0 0 0 0 5


TABLE3.

MODERN

CAPSICUM

SEED

ATTRIBUTEDATA,SORTED

BYSPECIES.

Seed

ID#

Genus

Species

Com

mon

Nam

eAssociatedCountry

Source

Seed

Shape

Maxim

umLength:Perpendicular

Width

1.1

Capsicum

annu

umKoriSitakame

Mexico/Southw

estU.S.

NativeSeedsSE

ARCH

Reniform

1.07

2.1

Capsicum

annu

umCoban

Mexico/Southw

estU.S.

NativeSeedsSE

ARCH

Reniform

1.14

3.1

Capsicum

annu

umDelArbol

Mexico/Southw

estU.S.

NativeSeedsSE

ARCH

Reniform

1.06

4.1

Capsicum

annu

umOrdono

Mexico/Southw

estU.S.

NativeSeedsSE

ARCH

Reniform

1.11

5.1

Capsicum

annu

umMirasol

Mexico/Southw

estU.S.

NativeSeedsSE

ARCH

Reniform

1.04

15.1

Capsicum

annu

umPinguitade

Mono

Peru

RefiningFireChiles

Reniform

1.13

29.1

Capsicum

annu

umUSD

A#215743

Hot

Peppers(Type1)

Peru

ReimerSeeds

Reniform

1.14

30.1

Capsicum

annu

umReimerUSD

A#439328

Hot

Pepper

Peru

ReimerSeeds

Reniform

1.15

31.1

Capsicum

annu

umInca

Berry

Hot

Peppers

Peru

ReimerSeeds

Reniform

1.18

32.1

Capsicum

annu

umInca

GlowHot

Peppers

Peru

ReimerSeeds

Reniform

1.22

36.1

Capsicum

annu

umUSD

A#241662

Peru

USD

AGermplasm

Bank

Reniform

0.99

37.1

Capsicum

annu

umUSD

A#257159

Peru

USD

AGermplasm

Bank

Reniform

1.12

38.1

Capsicum

annu

umUSD

A#257178

Peru

USD

AGermplasm

Bank

Reniform

1.17

39.1

Capsicum

annu

umUSD

A#439328

Peru

USD

AGermplasm

Bank

Reniform

1.11

40.1

Capsicum

annu

umUSD

A#439330

Peru

USD

AGermplasm

Bank

Reniform

1.06

41.1

Capsicum

annu

umUSD

A#439331

Peru

USD

AGermplasm

Bank

Reniform

1.14

42.1

Capsicum

annu

umUSD

A#439336

Peru

USD

AGermplasm

Bank

Reniform

1.33

43.1

Capsicum

annu

umUSD

A#439391

Peru

USD

AGermplasm

Bank

Reniform

1.02

44.1

Capsicum

annu

umUSD

A#640906

Peru

USD

AGermplasm

Bank

Reniform

1.24

7.1

Capsicum

baccatum

AjiAmarillo

Peru

AmazonasIm

ports

Oval

1.19

8.1

Capsicum

baccatum

AjiPanca

Peru

AmazonasIm

ports

Oval

1.21

13.1

Capsicum

baccatum

AjiAmarilloPepper

Peru

Trade

Winds

Fruit

Oval

1.15

14.1

Capsicum

baccatum

Aji

Peru

AndeanSeed

Collection

Oval

1.49

17.1

Capsicum

baccatum

AjiLemon

Peru

PepperLo

ver

Oval

1.21

21.1

Capsicum

baccatum

AjiPancaB

Peru

Peppermania

Oval

1.19

23.1

Capsicum

baccatum

Inca

Berry

Peru

Peppermania

Oval

1.23

24.1

Capsicum

baccatum

AjiChinchi

Amarillo

Peru

Peppermania

Oval

1.18

25.1

Capsicum

baccatum

Queen

LauriePI1281405

Peru

Peppermania

Oval

1.34

26.1

Capsicum

baccatum

Kaleidoscope

Peru

Peppermania

Oval

1.30

27.1

Capsicum

baccatum

Lemon

Drop

Peru

Peppermania

Oval

1.13

28.1

Capsicum

baccatum

AjiCristal

Peru

Peppermania

Oval

1.20


TABLE3.

(CONTIN

UED).

Seed

ID#

Genus

Species

Com

mon

Nam

eAssociatedCountry

Source

Seed

Shape

Maxim

umLength:Perpendicular

Width

9.1

Capsicum

chinense

AjiDulce

#2Pepper

Peru

Trade

Winds

Fruit

Circularwith

fishmouth

1.21

19.1

Capsicum

chinense

LimoBlanco

Peru

Peppermania

Circularwith

fishmouth

1.12

20.1

Capsicum

chinense

ScarletL

antern

Peru

Peppermania

Circularwith

fishmouth

1.33

22.1

Capsicum

chinense

AjiLimoRojo

Peru

Peppermania

Circularwith

fishmouth

1.32

6.1

Capsicum

frutescens

Tabasco

Mexico/Southw

estU.S.

NativeSeedsSE

ARCH

Teardrop

1.31

18.1

Capsicum

frutescens

AjiChu

ncho

Peru

PepperLo

ver

Teardrop

1.42

45.1

Capsicum

frutescens

USD

A#215728

Peru

USD

AGermplasm

Bank

Teardrop

1.19

46.1

Capsicum

frutescens

USD

A#260505

Peru

USD

AGermplasm

Bank

Teardrop

1.31

47.1

Capsicum

frutescens

USD

A#315007

Peru

USD

AGermplasm

Bank

Teardrop

1.30

10.1

Capsicum

pubescens

OrangeManzano

Pepper

Peru

Trade

Winds

Fruit

D-shape

1.20

10.2

Capsicum

pubescens

OrangeManzano

Pepper

Peru

Trade

Winds

Fruit

D-shape

1.19

11.1

Capsicum

pubescens

Red

Manzano

Pepper

Peru

Trade

Winds

Fruit

D-shape

1.32

12.1

Capsicum

pubescens

YellowManzano

Pepper

Peru

Trade

Winds

Fruit

D-shape

1.16

16.1

Capsicum

pubescens

Red

Rocoto

Peru

RefiningFireChiles

D-shape

1.04

Seed

ID#

Sphericity

TestaTexture

BeakProm

inence

BeakAngle

Attachm

entS

carSphericity

Avg.T

hick

Testa:A

vg.T

hinTesta

1.1

0.65

Smooth

toBroad

163

0.04

3.44

2.1

0.79

Smooth

toBroad

254

0.05

3.67

3.1

0.72

Smooth

toBroad

255

0.1

2.60

4.1

0.69

Smooth

toBroad

160

0.09

2.67

5.1

0.72

Smooth

toBroad

262

0.03

4.00

15.1

0.59

Smooth

toBroad

150

0.03

2.92

29.1

0.79

Smooth

toBroad

243

0.05

2.89

30.1

0.74

Smooth

toBroad

464

0.08

3.12

31.1

0.77

Smooth

toBroad

258

0.07

2.46

32.1

0.71

Smooth

toBroad

260

0.17

2.69

36.1

0.68

Smooth

toBroad

250

0.04

2.74

37.1

0.65

Smooth

toBroad

250

0.04

2.13

38.1

0.69

Smooth

toBroad

265

0.03

3.06

39.1

0.68

Smooth

toBroad

258

0.04

2.45

40.1

0.73

Smooth

toBroad

260

0.03

1.52

41.1

0.81

Smooth

toBroad

255

0.02

2.38


TABLE3.

(CONTIN

UED).

Seed

ID#

Sphericity

TestaTexture

BeakProm

inence

BeakAngle

Attachm

entS

carSphericity

Avg.T

hick

Testa:A

vg.T

hinTesta

42.1

0.59

Smooth

toBroad

240

0.02

3.08

43.1

0.64

Smooth

toBroad

155

0.09

3.36

44.1

0.65

Smooth

toBroad

253

0.08

2.67

7.1

0.83

Tight

reticulation

430

0.03

2.84

8.1

0.75

Tight

reticulation

46

0.01

3.14

13.1

0.75

Tight

reticulation

412

0.08

4.89

14.1

0.52

Tight

reticulation

5-10

0.01

5.85

17.1

0.72

Tight

reticulation

311

0.05

4.23

21.1

0.74

Tight

reticulation

37

0.03

4.23

23.1

0.72

Tight

reticulation

48

0.02

2.73

24.1

0.74

Tight

reticulation

415

0.04

3.50

25.1

0.6

Tight

reticulation

422

0.02

2.73

26.1

0.6

Tight

reticulation

410

0.02

4.82

27.1

0.74

Tight

reticulation

430

0.02

4.44

28.1

0.74

Tight

reticulation

420

0.02

3.20

9.1

0.78

Smooth

toBroad

463

0.06

5.11

19.1

0.79

Smooth

toBroad

468

0.3

3.78

20.1

0.65

Smooth

toBroad

452

0.09

5.64

22.1

0.68

Smooth

toBroad

448

0.07

4.67

6.1

0.64

Smooth

toBroad

474

0.05

2.94

18.1

0.54

Smooth

toBroad

470

0.06

4.75

45.1

0.72

Smooth

toBroad

467

0.04

4.14

46.1

0.63

Smooth

toBroad

470

03.10

47.1

0.61

Smooth

toBroad

475

0.04

4.00

10.1

0.63

Dramaticreticulation

328

0.02

8.53

10.2

0.8


10

0.06

7.73

11.1

0.57


34

0.01

6.50

12.1

0.69


110

0.04

7.77

16.1

0.85


126

0.06

5.92


species–level Capsicum identification that is anal-ogous in function to a dichotomous key, laid out inFig. 13.

SUMMARY OF MODERN CAPSICUM SEEDIDENTIFICATION

This guide utilizes the diagnostic traits ofCapsicum seeds (both quantitative and qualitative)and is meant to facilitate archaeological seed identi-fication. We have left out seed sphericity andML:PW because they are only useful when used aspart of a group of attributes. Non–diagnostic attri-butes for specific species are indicated by the ab-sence of boxes in Fig. 13. Based on our analysis, thefollowing are descriptive summaries of the uniquecharacteristics of each Capsicum taxon that corre-spond to Fig. 13.

Identifying Capsicum annuum Seeds

C. annuum seeds tend to be more reniform orkidney–shaped with a small protruding beak thatextends approximately 50°–65° from the seed body.Out of all the Capsicum domesticates, C. annuumhas the smallest thick testa to thin testa ratio, mean-ing that the margins of the testa thickness are closein size to the dorsal and ventral thickness.C. annuum, like C. chinense and C. frutescens, alsoexhibits a very smooth testa texture, with little to noreticulation.

Identifying Capsicum baccatum Seeds

C. baccatum seeds are primarily oval in shapewith a prominent, elongated beak. The attachmentscar is most often linear in shape, with a sphericity

Fig. 12. Examples of margins (transverse cross–section) of seed testa for the five domesticated Capsicum taxa.

Fig. 11. Examples of attachment scar sphericity for the five domesticated Capsicum taxa.


value averaging 0.01. While the testa texture ofC. baccatum is reticulated, the reticulation occursin a much tighter pattern than in C. pubescens.

Identifying Capsicum chinense Seeds

C. chinense is generally circular in shape with a“fish mouth” attachment opening that comprisesthe beak protruding at a wide angle and a small“lip” beneath it. The beak is generally prominent(medium) and the attachment scar shape is alsomore circular, hence the large attachment scar sphe-ricity (with an average value of 0.12). C. chinenseexhibits a smooth surface texture with little hint ofreticulation at the epidermal level.

Identifying Capsicum frutescens Seeds

C. frutescens is “teardrop”–shaped with a protrud-ing beak that forms the tip of this particular shape.Its beak is relatively prominent (medium) and it isdistinguished by the high beak angle (>67°). Its testatexture is generally smooth, much like C. chinenseand C. pubescens.

Identifying Capsicum pubescens Seeds

C. pubescens is easily distinguished in modernseeds by its black seed color while all the others arenaturally yellow or tan. Its shape generally resemblesthat of an oval or the letter “D.” C. pubescens seedsare also characterized by very thick margins andgenerally have the greatest thick testa to thin testaratio. The surface of C. pubescens seeds is also highlyreticulated, with uniquely dramatic reticulationaround the seed marg in . Fur thermore ,C. pubescens displays little to no beak protrusion.

Conclusion

From the data presented above, we determined thatCapsicum seed identification is possible using the sixquantitative and two qualitative attributes discussedabove. As can be seen in Fig. 10, the species groupsremain mostly separate, even among the membersin the C. annuum–C. chinense–C. frutescens com-plex, which some have argued should be subsumedunder a single species (Eshbaugh 2012). Thoughour research does not necessarily support the

Fig. 13. Guide to identifying Capsicum domesticates using diagnostic attributes.


validity of these separate taxonomic designations, itis worth noting from an archaeobotanist’s perspec-tive that seeds from these taxa are less distinctivelooking than C. baccatum and C. chinense. It is alsoworth adding that when applying our identificationguide developed from modern, dried chile pepperseeds to seeds recovered from archaeological con-texts, there are other issues to contend with, such aspreservation of diagnostic parts of the seed, tapho-nomic processes such as carbonization, and seedbrowning (Chiou and Hastorf 2012; Boonsiriet al. 2007; Lee et al. 1991; Minnis and Whalen2010). Minnis and Whalen (2010), for example,experimented with the effects of charring (the statein which most archaeobotanical macroremains arepreserved outside of areas with unique preservationconditions such as deserts) on Capsicum spp. seedsand found that the variation in size change was 10%to 69%, with cultivated seeds averaging a 27%decrease in seed size and wild seeds averaging a22% decrease in seed size. Thus, for those consid-ering application of our identification guide toarchaeobotanical material, it would be worth keep-ing those factors in mind.

This development of an identification system forCapsicum seeds will allow for archaeologists,archaeobotanists, and botanists to identify well–preserved archaeological seeds to species–level.Using this method, archaeologists can pursue suchCapsicum–related topics as determining how selec-tive pressures on chile peppers shifted through time,how specific cultivars of Capsicum moved from theorigin of domestication to other regions, and deter-mining the path of chile peppers around the worldfollowing the arrival of Europeans in the Americas.In terms of future work, we will continue addingdata from seeds of modern domesticates to enrichour data base as well as incorporate seeds from wildCapsicum species such asC. baccatum var. baccatum,C. baccatum var. praetermissum, C. eximium, C.tovarii, C. galapagoense, C. chacoense, etc. Data fromthese wild taxa could help untangle the complexstory of the chile pepper domestication.

AcknowledgmentsWe would like to thank Professor Tom D.

Dillehay for initiating our work on Capsicum.Araceli Aguilar–Meléndez was the original inspira-tion for a systematic study of these plants. Weacknowledge Dr. Guanwei Min’s training and ad-vice concerning SEM imaging of the Capsicumseeds. Special thanks to the USDA Germplasm

Resources Information Network (USDA–GRIN)and especially Dr. Mark Bohning, Dr. Bob Jarret,and Tiffany Fields for helping us find rarer speci-mens of Capsicum. Our chile pepper seed vendors,and in particular Beth Boyd from Bayou Traders,worked with us to obtain various Capsicum species.We also thank our peers in the McCownArchaeobotany Laboratory, especially AlanFarahani, Rob Cuthrell, and Theresa Molino foroffering advice and critical insight into our project.Alan Farahani, in particular, assisted us with statis-tics and commented on our drafts. We would espe-cially like to acknowledge the helpful commentsfrom our anonymous reviewers contacted by Eco-nomic Botany who aided in improving ourmanuscript.

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