## Abstract

Background Phytoliths (microscopic opal silica particles produced in and between the cells of many plants) are a very resilient, often-preserved type of microfossil and today, phytolith analysis is widely used in palaeoenvironmental studies, botany, geology and archaeology. To date there has been little standardization in the way phytoliths are described and classified.

Scope This paper presents the first International Code for Phytolith Nomenclature (ICPN), proposing an easy to follow, internationally accepted protocol to describe and name phytoliths.

## INTRODUCTION TO THE INTERNATIONAL CODE FOR PHYTOLITH NOMENCLATURE 1.0 (ICPN 1.0)

A discussion on phytolith nomenclature arose during the 3rd International Meeting on Phytolith Research (IMPR) in Bruxelles (August, 2000). The majority of the delegates agreed that standardizing and harmonizing the naming and describing of phytoliths would improve communication between researchers and facilitate the comparison of phytolith types and analyses. Presently, those studying phytoliths are faced with a considerable volume of names, including countless numbers of synonyms and homonyms. To further complicate the situation, there are often inconsistencies in the application of these names. The number of people working with phytoliths is growing fast, as is the exchange of data and communication between research groups. Standardizing the nomenclature is therefore urgently needed to avoid further confusion and allow easy, uniform and correct usage of phytolith names. Such stability can only be achieved by the application of a generally accepted (international) nomenclature protocol and glossary.

For this purpose, during the 3rd IMPR and with the sponsorship of the Society for Phytolith Research (SPR), a working group in charge of developing an International Code for Phytolith Nomenclature (ICPN) was created. The International Working Group on Phytolith Nomenclature (IWGPN) was to develop:

1. A standard protocol to be used during the process of naming and describing a new (or already known) phytolith type.

2. A glossary of descriptors (nouns and adjectives) to be used in naming and describing a phytolith type.

It is anticipated that the work of the IWGPN will be refined and the protocol and glossary improved by an ongoing committee appointed by the SPR. The standard protocol and glossary of descriptors developed by the first Working Group are presented here as the International Code for Phytolith Nomenclature 1.0.

The protocol suggested below follows the example of many other protocols already in use in other scientific disciplines. The protocol supplies the researcher with clear, easy-to-follow guidelines to apply when describing and naming a new or already published phytolith type. In cases where a phytolith type has been described in earlier works using a different terminology, citations of the earlier works should be included.

The publication of a new phytolith type requires two elements: an accurate description and an appropriate name.

## PHYTOLITH DESCRIPTION

### 1. Descriptive tools

The nouns and adjectives supplied in the Glossary at the end of this paper should be used. These are called descriptors. To ensure the utility of the Glossary by the international community, terms with Latin or ancient Greek roots are used. The Glossary will be updated regularly by the current IWGPN and future committees, and new descriptors may be added when necessary.

### 2. Description procedure

When describing a phytolith type, certain kinds of characteristic information need to be supplied.

#### Shape

A description of shape using terms from the Glossary or from geometrical forms should be supplied. The 3D phytolith form should be observed and described. Analysis in liquid mounting should be performed to facilitate the rotation of the phytoliths in this process and to ensure that all orientations are observed and described. Distinctive 2D characteristics should also be included in the description.

#### Texture and/or ornamentation

A description of distinctive ornamentation should be given using the terms supplied in the Glossary. Weathering features should not be described as ornamentations or texture but can be noted if distinctive. Presence of inclusions may be described, although they are not generally considered diagnostic.

#### Symmetrical features

Distinctive lines of symmetry should be included in the description.

#### Morphometric data

Measurements of size and shape with descriptive statistics, such as ranges and means, may be included in the description if an adequately large sample has been analysed. To verify that a statistically sound population has been sampled, a calculation such as the one below is recommended:

$n_{\mathrm{min}}\ =\ z_{{\alpha}/2}^{2}\ s^{2}/e^{2}$
Where nmin = minimum adequate sample;
$$z_{{\alpha}/2}^{2}\ =\ 1{\cdot}64$$
, which is the square of the two-tailed Z-value at α = 0·10; s2 = variance; and e2 = square of the desired margin of error, usually 0·05 times the sample mean.

#### Illustrations

Description of a phytolith type must be accompanied by illustrations. Illustrations need to be optical microscope photographs and/or 3D detailed line drawings portraying all possible orientations of the phytolith. Scanning electron microscope photographs can also be used as a complement to the main illustrations; but because most of the routine work in phytolith identification is done at the optical microscope, SEM photographs should not be used as a substitute for optical photographs. All illustrations must show a scale bar and a note with magnification and authorship.

#### Anatomical origin

The description of a phytolith type needs to explicitly state the anatomical origin of the phytolith (at tissue structure or cell level) only if the phytolith type has been directly observed in situ or if this origin has been already clearly demonstrated in previous, fully-referenced publication(s).

### 3. Taxonomic significance

Researchers should use caution in assigning taxonomic significance to a phytolith type. A phytolith type may be observed in a given taxon, but to be diagnostic it must be exclusively present in that taxon (e.g. if a phytolith type is considered diagnostic at family level, it must occur in all the genera of that particular family, and be absent in other families belonging to the same order or group). Geographically observed types can also be identified when the flora of a specific geographic area has been investigated (e.g. Tropical Africa, New World Tropics, etc).

The Working Group is very aware that, because of multiplicity and redundancy (Piperno, 1988), such an unequivocal production can often be impossible or very time-consuming to verify. When a phytolith type is observed in a plant and there is not sufficient information to corroborate any wider taxonomic significance, the researcher should avoid generalizations. For example, if a phytolith is observed in a species but no other comparative studies are available, then the phytolith should be published as observed in that species and not as diagnostic of that species or genus, family, etc:

• observed: found in a taxon but maybe present in other taxa;

• diagnostic: only present in that particular taxon.

#### Note I

When taxonomic significance cannot be assigned to a single phytolith type, a group of phytolith types and their frequencies (phytolith assemblage) may have taxonomic significance and this should be considered.

#### Note II

Silica skeletons (articulated phytoliths) maintain the cell architecture of the original tissue. The single cells forming the silica skeleton can be described using the same procedure as for single cells. A description of the silica skeleton using anatomical terms for the articulated cells (e.g. stomata, hair, papillae, etc) may also be useful.

## NAMING

### 1. Naming a phytolith type

The name given to a particular phytolith type should be formed by a maximum of up to three descriptors. Each descriptor can be a single word or a combination of words listed in the following order.

1. The first descriptor should describe the shape (this can be a 3D or a 2D descriptor whichever is more indicative and it can also include the symmetry, if indicative). The main orientation used when naming the phytolith type should be illustrated in the publication.

2. The second descriptor should describe the texture and/or ornamentation if characteristic or diagnostic and if not an artifact of weathering. Weathering features should not be described as surface ornamentation and they should not be part of the name. However, distinctive weathering features may be noted in the description.

3. The third descriptor should be the anatomical originwhen this is clear and beyond doubt. When the descriptor for anatomical origin also conveys a shape then an additional shape descriptor may not be needed. For example, ‘bulliform’ is a word established in the botanical literature to describe a particular type of cell found in the epidermis of the grass leaf. For this particular case, the word conveys both an anatomical—that particular cell in the grass leaf—and a descriptive meaning—the cell is shaped like a bubble/drop.

A preliminary list of common phytolith types together with their names following the ICPN rules and coding is given in Table 1.

Table 1.

Naming after ICPN: examples

*

Several drawings are made after Fredlund and Tieszen (1994).

Table 2.

Nomina conservanda

*

Several drawings are made after Fredlund and Tieszen (1994).

#### Nomina conservanda

Exceptionally, a name commonly used and made by descriptors not included in the Glossary can be preserved such as when a name has become so meaningful and internationally accepted that changing it might create confusion. The nomina conservanda rule will be applied in very exceptional cases at the discretion of the ICPN Working Group. The following is a list of nomina conservanda names accepted by the first ICPN Working Group:

• bulliform

• papillae

• dendritic

• cross

• rondel.

### 2. Publication of the name

A phytolith type named according to the International Code for Phytolith Nomenclature is considered the published name when the article has been distributed on printed matter to the general public (e.g. peer-reviewed journals, books or proceedings). Publication is not fulfilled by communication at a public meeting (e.g. conference), by web publication, by naming reference collection material or by the issue of microfilms made from manuscripts, typescripts or other unpublished material (e.g. university theses).

## GLOSSARY

Here is presented a first draft of the Glossary of descriptors (nouns and adjectives) for the description and naming of phytolith types. This Glossary is partially based on Bowdery et al. (2001). The descriptors used in the Glossary have a Greek or Latin root. This is to facilitate translation in as many languages as possible without loosing the original meaning. Some descriptors are accompanied by simple, schematic line drawings (patterns can be regular or not).

The descriptors are divided into several categories to facilitate the use of this Glossary.

• 1. First descriptors: shape

• 1a. Descriptors for 3D shape

• 1b. Descriptors for plannar or 2D shape

• 2. Second descriptors: texture and ornamentation

• 3. Third descriptors: anatomical

• 4. Other descriptors

• 5. Prefixes

1. First descriptors: shape

2. Second descriptors: texture and ornamentation

3. Third descriptors: descriptors for anatomical terms

4. Other descriptors

 abaxial away from the axis or central line abbreviated shortened abnormal(ly) departing from the usual abrupt terminating quickly accentric off-centre; cf. eccentric acuminate taper-pointed; gradually terminating to a point acute sharp-pointed; terminating quickly to a sharp point adaxial towards the axis or centre alate winged ampliate enlarged angulate with angles anterior front; on the front side apex point or tip articulated joined; attached asymmetrical(ly) lack of correspondence in the shape of parts on opposite sides of a plane (plane of symmetry may be specified) attenuate tapering base having to do with the part upon which something stands or rests bifid cleft in the middle bisected completely divided into two parts bulbous having a round, enlarged bulb at the end central in the middle compressed flattened lengthwise concave surface curved inwards in the middle continous unbroken; having the parts in immediate connection contorted twisted or bent convex surface curved outwards in the middle depressed flattened vertically disarticulated not joined; separated dorsal(ly) having to do with the higher (top) surface gibbous very convex horizontal(ly) in a plane parallel to the horizon interrupted broken; intermittent lateral(ly) having to do with the side margin edge marginal having to do with the edge obtuse blunt planar horizontally level or flat posterior at or toward the back reflexed curved segmented having internal divisions or sections solid having the interior filled up, not hollow, free from cavities symmetrical(ly) having correspondence in the shape of parts on opposite sides of a plane (plane of symmetry may be specified) tenuis slender, thin terminal having to do with the end transverse lying across the body truncate terminating abruptly, as if broken off ventral(ly) having to do with the lower (or anterior) surface vertical(ly) perpendicular to do the plane of the horizon
 abaxial away from the axis or central line abbreviated shortened abnormal(ly) departing from the usual abrupt terminating quickly accentric off-centre; cf. eccentric acuminate taper-pointed; gradually terminating to a point acute sharp-pointed; terminating quickly to a sharp point adaxial towards the axis or centre alate winged ampliate enlarged angulate with angles anterior front; on the front side apex point or tip articulated joined; attached asymmetrical(ly) lack of correspondence in the shape of parts on opposite sides of a plane (plane of symmetry may be specified) attenuate tapering base having to do with the part upon which something stands or rests bifid cleft in the middle bisected completely divided into two parts bulbous having a round, enlarged bulb at the end central in the middle compressed flattened lengthwise concave surface curved inwards in the middle continous unbroken; having the parts in immediate connection contorted twisted or bent convex surface curved outwards in the middle depressed flattened vertically disarticulated not joined; separated dorsal(ly) having to do with the higher (top) surface gibbous very convex horizontal(ly) in a plane parallel to the horizon interrupted broken; intermittent lateral(ly) having to do with the side margin edge marginal having to do with the edge obtuse blunt planar horizontally level or flat posterior at or toward the back reflexed curved segmented having internal divisions or sections solid having the interior filled up, not hollow, free from cavities symmetrical(ly) having correspondence in the shape of parts on opposite sides of a plane (plane of symmetry may be specified) tenuis slender, thin terminal having to do with the end transverse lying across the body truncate terminating abruptly, as if broken off ventral(ly) having to do with the lower (or anterior) surface vertical(ly) perpendicular to do the plane of the horizon

5. Prefixes

 a- without or lacking ab- away from ad- to or toward bi- two dis- between or away from hyper- above or beyond hypo- below inter- between poly- many semi- half sub- below, nearly, almost
 a- without or lacking ab- away from ad- to or toward bi- two dis- between or away from hyper- above or beyond hypo- below inter- between poly- many semi- half sub- below, nearly, almost

Many researchers have contributed, in one way or another, to the development of this project. First of all, we thank all the colleagues (too many to list them) that were at the session on phytolith systematics of the 3rd International Meeting on Phytolith Research held in Bruxelles (Belgium). There the seminal idea for this work saw the light and we had very emotional but nonetheless incredibly fruitful discussions on how to describe and name phytoliths in a standardized way that could be acceptable for all of us with different research backgrounds, from archaeology to palaeoecology and from botany to geology, and with different mother tongues. After the meeting, many colleagues read draft copies of the ICPN and of the glossary, forwarding valuable comments and ideas. We would like to thank R. M. Albert, L. Scott-Cummings, D. Pearsall (and her lab), D. Piperno, L. Vrydaghs, D. Zurro for their feedback and D. Bowdery and L. Wallis for discussing with us a descriptive tool they developed for their research in Australasia and for sharing their views and ideas on phytolith description and systematics. M. M. also thanks M. Osterrieth for inviting him to participate in the 2nd Meeting of Phytolith Research of the Conosur (Argentina, 2001) where fruitful discussions on phytolith nomenclature were held, especially with M. Osterrieth and A. Zucol. We express our gratitude to J. J. Motte for drawing the glossary illustrations and to J.-P. Theurillat for invaluable comments on the very final draft. The comments of V. Thorn and two other anonymous reviewers were much appreciated and greatly helped in ameliorating the paper.

## LITERATURE CITED

Bowdery DB, Hart D, Lentfer C, Wallis LA.
2001
. A universal phytolith key. In: Meunier JD, Colin F, eds. Phytoliths: applications in Earth science and human history. Rotterdam: Balkema, 267–278.
Fredlund GG, Tieszen LT.
1994
. Modern phytolith assemblages from the North American Great Plains.
Journal of Biogeography

21
:
321
–335.
Piperno DR.
1988
.Phytolith analysis, an archaeologucal and geological perspective. San Diego: Academic Press.

## Author notes

1Department of Archaeology and the McDonald Institute, Downing Street, Cambridge CB2 3DZ, UK, 2CNRS, CEREGE, Europôle de l'Arbois, BP80, 13 545 Aix en Provence Cedex 04, France and 3375 A Joseph Smith Building, Brigham Young University, Provo, UT 84602, USA