Maize can still be identified using phytoliths: response to Rovner

Maize can still be identified using phytoliths: response to Rovner

Deborah M. Pearsalla*, Karol Chandler-Ezellb, Alex Chandler-Ezellc

aDepartment of Anthropology, 107 Swallow Hall, University of Missouri, Columbia, MO 65211, USAbPsychiatry, MPE Program, Washington University, St Louis, MO 63108, USA

cDepartment of Curriculum and Instruction, University of Missouri, Columbia, MO 65211, USA

Received 17 September 2003; received in revised form 20 November 2003; accepted 23 November 2003

Abstract

In his comment on Pearsall et al.’s (J. Archaeol. Sci. 30 (2003) 611) study of maize cob phytoliths, Rovner claims to demonstratethat systematic errors in research design (the “transparent blindfold” of his title) led to the results reported. Error plays a role in thisexchange, but it is all on Rovner’s side. The central argument of his comment is based on his misreading and misuse of two tablesin our article, and a table published by Piperno and Pearsall (Smithsonian Contributions to Botany 85 (1998b)). Rovner confusesthe distinctive wavy-top and ruffle-top rondels produced by maize with simple mirror-image rondels produced by many grasses. Healso misunderstands the published work of early phytolith researchers, and attributes to them conclusions about phytolith formationthat they do not hold. Our conclusions do hold: maize cob phytoliths are distinguishable from teosinte (wild Zea) and most otherwild panicoid grasses of Mesoamerica. This research reaffirms the strength of typological approaches that incorporate thethree-dimensional morphology of phytoliths.� 2003 Elsevier Ltd. All rights reserved.

Keywords: Phytoliths; Zea mays; Typology; Blind testing; Systematic error; Replication

1. Introduction

In a misguided and inaccurately researched commenton our paper [17] Rovner [28] makes a two-part argu-ment. First, he claims that our research design is lacking,and that sample selection essentially negates the resultsof the blind test reported in the paper, calling intoquestion the method of identifying maize by cobphytoliths presented there. He further claims that3-dimensional morphology of short cell phytoliths hasnothing to do with the taxonomic relationships ofplants, and that no identifications can be made on thisbasis. The first complaint is based upon incorrect read-ing of the data tables and text in our article and inPiperno and Pearsall [25] as well as unsupportedassumptions about our methodology made by Rovner.The second is founded upon a series of funda-mental misunderstandings of plant anatomy, phytolithassemblages in grasses, and phytolith morphology. We

will first clarify the points misunderstood by Rovner,and then respond to each of his two complaints in turn.

2. Clarification of tables describing phytolithdistributions

Let us begin by clearing up the misreading and misuseof data that forms the bulk of Rovner’s comment.Rovner makes extensive use of three tables, two fromour paper [17], Table 2, the grasses in our samplepopulation that produced the diagnostic inflorescencephytoliths that were the focus of the paper, and Table 4,the key used during the blind-testing, and one table fromPiperno and Pearsall [25], Table 1, the summary ofphytolith production patterns in Neotropical grasses.Rovner misunderstands and misrepresents these tables.Our Table 2, which is reproduced in part as the top ofFig. 1, presents only the results of K. Chandler-Ezell’sscanning of a large population of grasses for thediagnostic inflorescence phytoliths that were the target ofthe study. These included the wavy-top rondel, which isrecognized and used as a maize diagnostic [5,6,14].

* Corresponding author. Tel.: +1-573-882-3038;fax: +1-573-884-5450.

E-mail address: [email protected] (D.M. Pearsall).

Journal of Archaeological Science 31 (2004) 1029–1038

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Chandler-Ezell observed a variety of phytoliths in thegrasses she scanned, but did not tally all of them: thatwas not our goal. Table 4, which is reproduced in part asthe bottom of Fig. 1, is the key used in the blind-tests: itis based on these same inflorescence phytoliths (comparethe headings in Table 2 and the choices in the key inTable 4: they are the same). Notice that three different

kinds of rondels (short cells with circular to oval bases)are included in this group: wavy-top rondels, ruffle-top rondels, and half-decorated rondels. These areillustrated in Fig. 2.

By contrast, a broad overview of phytolith produc-tion in grasses was the goal of Piperno and Pearsall’s [25]earlier study. The first page of the large Table 1 from

Fig. 1. The top reproduces a section of Table 2 from Pearsall et al. [17], the bottom shows a section of Table 4 from that publication. The arrowspoint to three kinds of rondels included in these tables: wavy-top rondels, ruffle-top rondels, and half-decorated rondels. These are complex,decorated rondels produced by Zea.

D.M. Pearsall et al. / Journal of Archaeological Science 31 (2004) 1029–10381030

that article is reproduced as Fig. 3. Notice that theheadings of this table are quite different from the tablesin Pearsall et al. [17]. The arrow indicates the column forrondels. What are these? “In Table 1, the placement ofphytoliths under the saddle-, rondel-, bilobate, or cross-shaped category signifies that these bodies are of the

classic shapes that have been commonly reported inprevious grass studies. In other words, they are usuallytabular, mirror-image forms . ” [25], p. 2; emphasisours. Tabular, mirror image rondels (circular to ovalbases and flat tops) are illustrated in Fig. 4. These werenot the focus of the Pearsall et al. [17] study; they are not

Fig. 2. Examples of wavy-top rondels, ruffle-top rondels, and half-decorated rondels, which were the subject of the study by Pearsall et al. [17]. a:ruffle top rondel, side view, ruffled top is to the right; b: ruffle-top rondels, rondel faces are up (sharp focus), ruffled faces are down; c: wavy-toprondel, wavy top is to the right; d: wavy-top rondel, wavy top is up; e, f: half-decorated rondels.

D.M. Pearsall et al. / Journal of Archaeological Science 31 (2004) 1029–1038 1031

diagnostic of maize; our study has nothing to do withthese phytoliths. This fundamental misinterpretation byRovner of the data presented in our paper, and in theearlier study [25], underlies the bulk of his comment: heis speaking of distributions of mirror-image rondels(Fig. 4), we present an identification method based onwavy-top rondels, ruffle-top rondels, and half-decoratedrondels (Fig. 2), among other forms.

3. Project research design complaints

As we explained in our paper, the research designfor the project was set up by Pearsall and executed byK. Chandler-Ezell, who wrote the types and scanned thespecimens. The goal of the study was to determine ifmaize cob bodies, especially wavy-top and ruffle-toprondels (phytoliths with round to oval bottoms andcomplex tops) first identified in the early 1990s [5,14,23],could be distinguished from teosinte (other Zea speciesand varieties) and wild grasses likely to overlap withZea. We began with the existing maize cob rondel types,recognized and in use in North America and in restrictedcontexts elsewhere (e.g., [6,7,33]). We firmed up, ornarrowed, the identification criteria for these maize cobrondel types and also looked for other useful types bystudying a large population of maize varieties. Maize is

a panicoid phytolith-producing grass; wild Zea (teosintespecies and varieties) and other wild panicoid grasses arethe most likely to overlap with maize. Furthermore,panicoid grasses dominate the grass component ofvegetation both in lowland Mesoamerica, the region ofimmediate interest, and in general in the areas of themoist, warm Neotropics where Pearsall works. Most ofthe wild grass taxa studied were selected on this basisand thus included wild Zea taxa and genera of panicoidgrasses that occur in Mesoamerica according to regionalfloras. Inflorescence samples, rather than leaves, werestudied because the previously recognized types—wavy-top and ruffle-top rondels—are produced in maizeinflorescences, not leaves.

Rovner claims that this was not an appropriate testgroup of grasses, since our study revealed that few ofthese grasses produced types similar to maize cob bodies(!). This odd conclusion is elaborated in a long discus-sion of data from Piperno and Pearsall’s [25] overview ofphytolith production patterns in Neotropical grasses. Asalready discussed, Rovner misread that table andequated tabular, mirror image rondels with the wavy-top, ruffle-top, and half-decorated rondels that we werestudying. Rovner is unable to distinguish types or theirnames throughout his argument, confusing all rondels asbeing the same body. This inability to distinguish types,however, may be due to his insistence upon recalling

Fig. 3. The first page of Table 1 from Piperno and Pearsall [25]. The arrow points to the rondel column. These are tabular, mirror image rondels.


only a single 2-dimensional face of a diagnostic classthat leads, in turn, to a lack of experience and familiaritywith 3-dimensional types. A review of Rovner’s publica-tions confirms this impression. In the three publishedworks in which he presents his studies of phytolithproduction patterns in plants [27,29,31], the earlieststudy describes grasses in terms of broad classes ofshort cells they produce, and the later studies employan imaging technique that treats short cells as2-dimensional objects. There are no type-by-typedescriptions of the 13 species of grasses included in thesestudies. Confusion and lack of experience with3-dimensional types led Rovner to his erroneousconclusion that Pearsall selected grasses for the test thatwould not produce rondels that might overlap withmaize: “The statistical probability that this result couldoccur by chance is astronomically remote” [28].

What nonsense. The wild grass taxa were selected forthe study as described; the design and execution ofthe project are documented in K. Chandler-Ezell’slaboratory notebooks (#4, 9/99-8/00; #5, 8/00-4/01, #64/01-9/01, #7, 10/01-11/13/01, paper submission date).

All MU Paleoethnobotany laboratory documents andcollections are available for public scrutiny.

So, what about all the counts and percents of rondelsfrom this and that grasses gleaned by Rovner fromTable 1 of Piperno and Pearsall [25]? As explainedabove, the phytoliths tallied as rondels on that table arethe classic shapes that have been commonly reported byphytolith analysts since study of grasses began: tabular,mirror-image forms [25], p. 2. Such mirror-image rondelsoccurred in various of the grasses we studied for the2003 paper. For similar reasons, we did not list themyriad of other phytolith types common to panicoidsand grasses in general, despite their common occurrencein the samples. We didn’t tally mirror-image rondels forthe same reason we didn’t tally bilobates or epidermalcells, because these types were common to all or most ofthe samples and thus were not useful as species-leveldiagnostics of Zea. The focus of our study was thedecorated, complex rondels (rondel on one face, wavy orruffled on the other face) documented as being present inmaize cobs by ourselves and others [5,14,23]. Our goalwas to determine whether these wavy-top and ruffle-top

Fig. 4. Tabular, mirror image rondels, which were not the subject of the study by Pearsall et al. [17]. a, b: elongated tabular rondels, c: tall tabularrondel; d: group of rondels, including “spiked” rondels. Notice how distinctive “spiked” rondels are from wavy-top and ruffle-top rondels (Fig. 2).


rondels (and other types produced in maize) occurredin wild panicoid grasses. There is no possibility ofconfusing tabular, mirror image rondels with the formswe studied (compare Fig. 2 and Fig. 4).

Out of this confusion and misinterpretation of datatables on Rovner’s part comes the question of why thebamboos and canes known to produce potential con-fusers were not included in the blind test. This is alegitimate question. Nothing Machiavellian occurredhere, just a matter of timing that should have beenfootnoted in our paper. The maize, teosintes, and wildpanicoid grasses were studied, the types refined, andthe blind test designed by early February 2001(Chandler-Ezell lab notebook #5). The blind tests wererun at MU in March 2001 and at Washington Universityin May 2001 (Chandler-Ezell lab notebook #6). Thefinal results of the study to that date (the types, potentialoverlaps, “Big Pit” test, and blind study tests) werecompiled later that summer and shared with Dolores

Piperno. She scrutinized the types and suggested that wecheck Gynerium sagittatum and species of Guadua forpossible overlap. Piperno has made an exhaustive studyof grasses in the Arundinoideae and Bambusoideaesubfamilies, and only had concerns about possible over-lap from Gynerium sagittatum and Guadua (personalcommunication to Pearsall, recorded in Chandler-Ezelllab notebook #6; verified 9/17/03). In response toPiperno’s review, we went back to the regional floras inlate August 2001, and compiled a list of all nativeregional taxa in these two subfamilies. We sampled atleast one species per genus of bamboos and canes(including Gynerium sagittatum, and native bamboospecies transferred from Guadua to other genera). Westudied this whole new suite of grasses, not just the twotaxa recommended by Piperno, to err on the side ofcaution. The results are as reported in the paper; overlapwith maize is not a problem. We did not rerun the blindtests: we had been working on the project two years atthis point and wrote and submitted the paper.

Let us now turn to Rovner’s other criticisms of theresearch design of the blind tests. A misinterpretation ofthe blind testing was raised in the comments that [1] theunnamed “expert” who participated in the tests definedthe distinctions between rondels of maize and teosinte,and [2] identification was not “effectively replicated byany of the others in spite of persistent and determinedeffort” [28]. First of all, we have already restated thatK. Chandler-Ezell wrote the types, trained all test sub-jects, and set up the blind tests so that Pearsall (theunnamed expert) as well as the other subjects couldundergo truly blind testing. This was done to increasethe objectivity of the assessment of both the training andthe identification protocol. K. Chandler-Ezell was notone of the test subjects, of course. Secondly, the subjectswere trained (until they declared themselves ready)during the pre-trial period and then tested. The trialswere broken into three stages to deal with fatigue, butwere part of the same assessment period and performedwithout additional or supplemental training by K.Chandler-Ezell between trials. This does not constitute“persistent and determined effort.” Rather, it constitutesthe opposite: a single effort, i.e. one testing periodfollowing a single training period. The test results werenot graded, or even viewed, by K. Chandler-Ezell until asubject had completed the entire testing period to avoidaccidental feedback that could skew subject perform-ance. The tests were, in fact, quite successful, particu-larly when the relative inexperience of most of thesubjects is considered alongside their success at using anew system: correct classification at the genus level was84% for maize and 79% for teosinte, with no mis-identification of wild non-Zea grasses as Zea. Thenovice subjects had little or no experience with phytolithidentification prior to the training. A lack of 100%accuracy by subjects using a classification protocol for

Fig. 5. Articulated phytoliths from a teosinte fruitcase. The lowerimage is a magnified view of the upper image. The “a” arrow points tothe upper face of the rondel (sharp focus): this is the ruffle-top, whichextends out beyond the base. The “b” arrow points to the lower face ofthe rondel, which is the rondel base. Photograph courtesy of I. Holst,Smithsonian Tropical Research Institute, Panama.


the first time is no reason to conclude that taxonomicclassifications using visually prominent features are a“ ‘tyranny’ of subjective expert typology” [28]. Rejectionof any classification system that failed to perform toRovner’s criteria would require that all botanicalclassification be rejected on the grounds that mostfirst-year plant taxonomy students fail to perform to thestandards of their instructors on their first quiz. Anotherexample would be discarding projectile point classifica-tion because beginning archaeology students failed toclassify tools accurately using Bordes’s classificationsystem.

Rovner claims that using “pure types” in the tests wasa poor research design, because the assemblages mightgive “clues” to the grass’s identity. Of course they do,but this is not a flaw in the research design. The 1000s ofphytoliths visible in each comparative sample used in thetrials clearly indicated that they come from plants thatare monocots, grasses, and panicoid grasses. The entirebasis of the research was to differentiate a few taxa,namely the genus Zea, from other grasses. The typesused in the classification protocol were “diagnostic”types by definition because they did allow such adichotomous differentiation to be made. That is thefoundation of the concept of “diagnostic” types, theirutility in diagnosing the presence of the indicated taxon.

Secondly, pure types were used because this is a partof the classification process. This approach is basedupon well-established botanical research methodology.Type specimens are required to define types, and thosespecimens are “pure”—a member of only that taxon.One studies several examples of the type to get a rangeof variation within that taxon, then compares it tooutgroups, and finally writes a taxonomic descriptionthat can be used to separate individual items of thattaxon from other items. One doesn’t write a taxonomicdescription of dandelions from a sample of 200 differentflowers. One evaluates the plants to be separated, findsthe features that separate them, writes the types, teststhe system on more plants, and THEN moves on todistinguishing it from a mixed sample.

Finally, Rovner claims that the “pure” taxonassemblages used in the tests could not possibly simulatethe mixed taxon assemblages of open archaeologicalcontexts. He gives no support to this blanket statement;in our experience, archaeological phytolith assemblagesvary from simple to complex. The grasses scanned forthe tests provided considerable complexity for partici-pants to deal with, with dozens of bodies per field todistinguish. Rovner makes no suggestion for an alterna-tive approach to our design for the blind tests. Weknow of no way of creating test slides that only containcertain phytoliths, and photographs do not allow rota-tion of forms critical for applying the identificationprotocols. We addressed this problem in training,though. We simulated very simple sets of phytoliths with

3-D models: subjects were presented with increasinglycomplex and more difficult-to-distinguish sets of themodels as they were trained.

To summarize, we stand by our results and by theresearch design that produced them. Two of the mostimportant types used in our study, wavy-top andruffle-top rondels, are reliably recognized and routinelyused by researchers unconnected with the MU Paleo-ethnobotany lab. Our contribution was to begin theprocess of extending the use of these bodies to a widerarray of archaeological contexts. This is a well-knownpractice called the scientific method, in which oneformulates a hypothesis, then tests it by performingexperiments, making real observations, and evaluatingthe data.

4. Misconceptions about the structure and viewing of3-D characteristics of phytoliths

Anyone who has sat at a microscope and rotated“loose” phytoliths (by pressing on the cover slip with aprobe) knows phytoliths are 3-D objects. They aresometimes small, but recognizably 3-dimensional at400�. Look at slides of phytoliths extracted fromdifferent individuals of the same species, and you willsee the same kinds of 3-D objects. Flip throughedited volumes on phytolith analysis [10,13,18,26] orany number of journal articles (e.g., [1,5,9,12,30,33,34]):everyone with current training in paleoethnobotanyrecognizes and often uses the 3-D qualities of phytolithsto aid in classification. This is standard procedure. Twoexamples: “Three-dimensional morphology readily dis-criminated between corn cob chaff and the inflorescenceassemblages created by wild grasses, including that ofwild rice” [34], p. 9; “The more recent practice ofthree-dimensional viewing makes distinguishing betweenPanicoid bilobates and Stipeat pyramids less problem-atic because the cross-section of the Stipeat pyramid istrapazoidal, with the top being smaller than the base.”[12], pp. 286–287. Rovner’s comment that 3-D shape hasnothing to do with phytolith taxonomy is out-of-stepwith accepted practices in the discipline, and reflects hisunfamiliarity with the 3-D structure of phytoliths.

What is the best way to view this three-dimensionalstructure, with transmitted light microscopy (TLM), asin the research we have published, or scanning electronmicroscopy (SEM)? SEMs may produce larger images ofindividual phytoliths, but also result in substantial dis-advantages. You have a smaller sample, cannot rotatethe phytoliths to determine the total morphology (youcan capture several bodies in differing positions, butcannot rotate the same body), and cost prohibitsextensive sampling (reducing the reliability of yourresearch due to smaller sample sizes and researchpopulations). Worst of all, phytoliths coated for SEMare opaque—you only see the painted shell of the


phytolith. TLM is inexpensive, non-destructive, andutilizes liquid mounting media that allow for rotation tosee all faces of each body. Sample size is large. TLM alsosuspends phytoliths in a transparent solution and shineslight through the transparent phytoliths so the analystcan see the internal structure and other faces as well asthe “top” face. In TLM, the 3-D surface morphologiesof phytoliths are visible both directly (through rotation)and indirectly (through transparency).

In addition, 400� is quite visible for the featureswe use to distinguish diagnostics, such as total bodylength, width, outline, and protruding features. Thecomparison Rovner draws to the higher magnificationsnecessary to do some pollen identifications is spurious:diagnostic features used to identify pollen (such asdetailed structures of the exine) are an order of magni-tude smaller in scale than comparable diagnosticphytolith characteristics.

Phytoliths form by accretion of silica in some plantcells; this is a well-known fact. Rovner maintains thatthis formation process, and the orientation of phytolithsin cells in which they form (i.e., which phytolith face isup and which is down), somehow renders the resulting3-D morphology of phytoliths meaningless. A closeexamination of Rovner’s argument reveals the source ofthis puzzling assertion: Rovner does not understand,and misrepresents, the early literature on phytolithformation processes. Sangster [32], for example, is not astudy of the process of 3-D formation of phytoliths. It israther a study of the process of intercellular silicadeposition in leaves of four developmental stages(immature to senescent). It compares when tissues ofvarious kinds (long cells, bulliforms, abaxial silicabodies, and so on) silicify in the life cycle of the leaf, andpresents data on the density of silica deposited (mean #phytoliths/mm2 of tissue). There is no discussion of atwo-part silicification process for individual phytoliths, asRovner claims; the comparisons drawn in the study arebetween leaves of different ages, and the kinds oftissues that tend to silicify at different stages of leafdevelopment.

Rovner also misrepresents the Hayward and Perry[11] study. These authors discuss the shapes of phyto-liths formed in a variety of tissues, and describe andillustrate their 3-D structure. They discuss, for example,the shape of outer surfaces, cross sections, and inneredges of costal rods (what would now be called crenateshort cells) and hat-shaped opals, and say: “The opalinebodies appear to be derived directly by silicification ofthe walls and lumens of the idioblasts without majorchanges in shape occuring as a result of silicification”[11], p. 1005. The article’s illustrations show the 3-Dstructure of these clearly. Rovner’s confusion may arisefrom the subsequent discussion of silicification of vesselelements (not short cells), in which Hayward and Perrypostulate two mechanisms of silicification: silicification

of the secondary wall, and silicification of the lumen,which need not be filled with silica. It is in this contextthat the quote used by Rovner begins. The passage readsas follows, with passages omitted by Rovner (sentencesand phrases in italics) restored:

Lumina opals do not necessarily correspond with theshape of the enclosing cell if differential depositionof the secondary wall has taken place (Parry andSmithson, 1966) [16]. In any case it is difficult toimagine that cell shapes correspond exactly with theultimate shapes of the silica bodies when these areviewed three-dimensionally to illustrate their lobedand trough shaped appearances. However, costalsilica cells in the leaf blade do possess crenulate wallssimilar to the outline of the rods. While sections werenot made to determine whether the inner edges ofthe cell walls were also lobed, the isolated rods aregenerally five-sided and all the edges bear some degreeof crenulation. This degree of crenulation was not seenby Parry and Smithson (1964) [15] or Blackman(1971) [4]. The latter reports many rods to be triangu-lar in cross section when situated directly above thejunction of two hypodermal cells. It is conceivable thatthe precise location of wavy rods in relation to theunderlying tissues determine their shapes and degreeof crenulation [11], p. 1006.

Restoring the text omitted by Rovner restores Haywardand Parry’s observation that costal silica cells (i.e., shortcells, like maize cob rondels) do take on the 3-D struc-ture of the cells in which they form. Hayward andParry’s research does not demonstrate a lack of corre-lation between 3-D structure and short cell shape—quitethe opposite. Hayward and Parry’s point about preciselocation determining 3-D shape in short cells has beenconfirmed by later research. Piperno has demonstrated,for example, in her study of cross 3-D variants thatVariant 1 crosses are located over the veins, and Variant5/6s and 2s are located in between the veins in intercostalareas [19,21,22]. The point is that Hayward and Parrydo not discuss a two-stage silicification mechanism forphytoliths formed in idioblasts (i.e., short cells such asthe rondels under discussion here): there is no discussionof a first stage upper face, or a second phase lower face;no discussion of cytoplasm collapse on to the bottomphytolith face; no discussion of random variability in3-D structure.

Intercellular phytolith formation was studied in detailprimarily by Elizabeth Blackman in the late 1960s; herwork is considered seminal in this regard. Contraryto the mechanisms Rovner depicts, Blackman [2,3]observed how the cytoplasm of young silica cells com-pletely lost their cell contents before they were filled withsolid silica. She describes how “empty cells contain-ing neither protoplasm nor silica bodies are easilyobserved,” and that “loss of the cell contents is a


consistent feature in the development of silica cells.” [3],p. 836. Shortly after she observed these dead, emptycells, they were very rapidly filled with solid silica [3]. Torepeat, there is no two-stage silicification process involv-ing collapsed cytoplasm like the one described byRovner and attributed to these phytolith researchers.Furthermore, researchers of this period did not studyphytolith 3-D structure in any detail, and did notcomment on its utility as a taxonomic tool. Some ofthem recognized this attribute and were intrigued by it,however. Parry and Smithson [15], p. 172 in a seminalstudy of phytolith shape in the grass family commented:“These bodies are not as simple in shape as they appearto be in perfect surface preparations. Given a sufficientnumber of examples turned on their major axis througha variety of angles, (Plate I, Figs. 4, 6, 7, 14, 19, 20–22),it is possible to assess their true three-dimensionalshape.”

In addition to the fact that the discussions of shortcell silicification processes Rovner cites do not exist, hewould have us believe that consistency in 3-D shapes ofphytoliths are pure happenstance. In other words,Rovner proposes that phenotypes (the plant anatomyand morphology which form phytoliths) have nothingto do with genes. Such a fundamental lack of basicbotanical knowledge, misinterpretation of cited sources,and logical discrepancies is typical of the argumentsmade by Rovner in his comment.

In terms of Zea rondel bodies, Rovner further claimsthat the rondel face is the upper face of the phytolith,and the wavy or ruffle face the lower face. We checkedout this claim, and Rovner is mistaken. As Fig. 5illustrates, positioning of ruffle-top rondels in theteosinte fruit case is ruffled side up, rondel side down.This is also the case for maize leaf phytoliths—thenon-type tier (i.e., the side that defines the cross varient,19) is up while the standard cross face is down—and forthe unique short cell phytoliths found in some bamboos(I. Holst, personal communication, 10/03).

There is one additional case of Rovner misunder-standing and misrepresenting published research thatneeds to be addressed, his discussion of Piperno’sAguadulce research. His confusion of mirror imagerondels and complex Zea inflorescence rondels isrepeated in that discussion, and needs no further com-ment. He goes on to confuse the results of two studies atthe site. Piperno [20] identified cross-shaped phytolithsfrom maize leaves in ceramic-phase occupations (ca.5000–3000 B.P.) at the site. In a later study, described inPiperno and Pearsall [24], she reports maize cob phyto-liths from the site. Rovner asserts that the later resultsconflict with the earlier data. This assertion is puzzling:two different structures of the maize plant with twocompletely different sets of phytoliths were considered,and cob phytoliths were not identified during thefirst study because Piperno had not yet examined that

structure of the maize plant. (No one had studiedphytolith production in cobs at this time.) Obviously,glume hardness (a trait of the cob) cannot be addressedusing leaf phytoliths. Rovner’s misunderstanding ofsuch a basic point about the morphology of maize andmaize phytoliths illustrates again his lack of knowledgeand experience on this topic. Furthermore, Piperno doesnot argue that teosinte is present in Panama, as Rovnerclaims, but rather that a hard-glumed Zea not yet fixedat the critical tgal locus (which controls glume size andhardness, 8) was being grown during the preceramicperiod. Dramatic effects on phytolith morphologycaused by differing expressions of the tgal locus werefirst suggested by Dorweiler and Doebley [8], and havebeen further elucidated by detailed analyses of teosintefruitcases and homologous maize cupules and glumes(e.g., [5,14,17,23,34]).

5. Concluding remarks

It has been our unwelcome task to point out themisinterpretations of data, inaccurate discussions ofliterature, and poor understanding of phytolith forma-tion processes and three-dimensional morphologies thatled Rovner to claim that our research on maize cobphytoliths was erroneous. The errors are all on Rovner’sside: maize can still be identified using phytoliths. Wehave shown how most of his comment is based uponincorrect reading of the data tables and text in ourarticle and in Piperno and Pearsall [25], as well asunsupported assumptions about our methodology. Poorscholarship on Rovner’s part is further demonstratedby his misrepresentation of discussions of phytolithformation in important early sources, such as Haywardand Perry [11] and Sangster [32], and his attribution tothese scholars of non-existent discussions of short cellformation processes.

The maize cob phytolith study was done exactly asdescribed in Pearsall et al. [17]; no sleight of hand, nohidden agendas. It is a first step in identifying maizecob remains in a broader range of archaeological andpaleoecological contexts; research is already underwayto test its application in settings other than lowlandMesoamerica.

Acknowledgements

We thank R. A. Benfer, Jr and D. R. Piperno forhelpful comments on an earlier draft of this paper.NIMH Post-doctoral Fellowship support for K. C.-E.provided by National Institute of Mental Health(T32 MH17104), L. B. Cottler, P.I. Figures prepared byW. Grimm.


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Maize can still be identified using phytoliths: response to Rovner

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