PREFACE
 

Unambiguous names for organisms are essential for effective scientific
communication; names can only be unambiguous if there are internation-
ally accepted rules governing their formation and use. The rules that gov-
ern scientific naming in botany (including phycology and mycology) are
revised at Nomenclature Section meetings at successive International Bot-
anical Congresses. The present edition of the International code of botan_
ical nomenclature embodies the decisions of the XVII International Bot-
anical Congress held in Vienna in 2005 and supersedes the Saint Louis
Code, published six years ago subsequent to the XVI International Bot-
anical Congress in St Louis, Missouri, U.S.A. It is written entirely in
(British) English. The St Louis Code was translated into Chinese, French,
Japanese, Portuguese, Russian, Slovak, and Spanish; it is therefore antici-
pated that the Vienna Code, too, will become available in several lang-
uages in due course.

One of the reasons invoked for the choice of Vienna as the site of the sev-
enteenth Congress, was that the second International Botanical Congress
had been held there exactly 100 years earlier. It was that Congress that
accepted the first internationally developed rules governing the naming of
plants, Règles internationales de la Nomenclature botanique adoptées par
le Congrès International de Botanique de Vienne 1905 / International
rules of Botanical Nomenclature ... / Internationale Regeln der Botan-
ischen Nomenclatur ... – or simply the Vienna Rules, thus obviating con-
fusion with this Vienna Code, and not requiring this Code to bear any
qualifying numeral.

The Vienna Code does not differ substantially in overall presentation and
arrangement from the St Louis Code, and the numbering of Articles re-
mains the same, although there have been a few additions to, and modi-
fications of, paragraphs, Recommendations, and Examples, often involv-
ing changes in their numbering. One small change has also been made in
the numbering of the Appendices to make this more logical: the former
App. IIIA, dealing with conserved names of genera is now simply App.
III, and the former App. IIIB, with names of species, becomes App. IV.
With App. IIA & IIB continuing to contain the two sorts of conserved
family names, there is now a logical sequence for the lists of conserved
names: II for families, III for genera, and IV for species. The subsequent
Appendices increase in number accordingly, so that names rejected “uti-
que” under Art. 56 form App. V, and suppressed works, App. VI. The St

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Louis Code omitted the “Important Dates in the Code” that had appeared
in the Berlin & Tokyo Codes; this has been restored in the Vienna Code,
from a draft by D. L. Hawksworth.

In overall presentation the most notable feature, however, is the inclusion
for the first time of a Glossary, which appears as Appendix VII. This was
requested by the Vienna Congress and it was made clear that it should be
an integral part of the Code with all the authority thereof. This has meant
that the Glossary is very tightly linked to the wording of the Code, and
only nomenclatural terms defined in the Code can be included. A few oth-
er terms in more general use and not defined in the Code (e.g. description,
position, rank) but with distinctive application in the Code have, however,
also been included; they are distinguished by the statement “not defined”
followed by an explanation of the way in which, in the opinion of the
Editorial Committee, they are applied in the Code. For the preparation of
the Glossary, the Committee is particularly grateful to P. C. Silva, who ini-
tiated the project and who prepared the first draft for consideration by the
Editorial Committee and who has worked over several subsequent ones,
ensuring precision and consistency.

The text of the Code uses three different sizes of print, the Recommen-
dations and Notes being set in smaller type than the Articles, and the
Examples and footnotes in smaller type than the Recommendations and
Notes. The type sizes reflect the distinction between the rules which are
mandatory (Articles), complementary information or advice (Notes and
Recommendations), and explanatory material (Examples and footnotes).
A Note has binding effect but does not introduce any new provision or
concept; rather, it explains something that may not at first be readily
apparent but is covered explicitly or implicitly elsewhere in the Code.
Some Examples, which were deliberately agreed by a Nomenclature Sec-
tion, contain material which is not fully, or not explicitly, covered in the
rules. Such “voted examples” are prefixed by an asterisk (*). If, by a
change of the corresponding provision in a subsequent edition of the
Code, a “voted example” becomes fully covered, the asterisk is removed.

As in the previous edition, scientific names under the jurisdiction of the
Code, irrespective of rank, are consistently printed in italic type. The Code
sets no binding standard in this respect, as typography is a matter of
editorial style and tradition not of nomenclature. Nevertheless, editors and
authors, in the interest of international uniformity, may wish to consider
adhering to the practice exemplified by the Code, which has been well
received in general and is followed in a number of botanical and myco-

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logical journals. To set off scientific plant names even better, the aban-
donment in the Code of italics for technical terms and other words in
Latin, traditional but inconsistent in early editions, has been maintained.

Like its forerunners, the Editorial Committee has tried hard to achieve
uniformity in bibliographic style and formal presentation – a sound educa-
tional exercise for its members, and a worthwhile goal because the Code is
considered a model to follow by many of its users. The titles of books in
bibliographic citations are abbreviated in conformity with Taxonomic lit-
erature, ed. 2, by Stafleu & Cowan (1976-1988; with Supplements 1-6 by
Stafleu & Mennega, 1992-2000), or by analogy, but with capital initial
letters. For journal titles, the abbreviations follow the Botanico-peri-
odicum-huntianum, ed. 2 (2004).

Author citations of scientific names appearing in the Code are standard-
ized in conformity with Authors of plant names, by Brummitt & Powell
(1992), as mentioned in Rec. 46A Note 1; these are also adopted and
updated by the International Plant Names Index, and may be accessed at
http://www.ipni.org/index.html. One may note that the Code has no tradi-
tion of recording the ascription of names to pre-1753 authors by the valid-
ating author, although such “pre-ex” author citations are permitted (see
Art. 46 Ex. 33).

Like its immediate predecessor, the Vienna Congress was conservative in
nomenclatural matters in comparison with some earlier Congresses. Rela-
tively few changes were accepted, but a small number of significant ones
and many useful clarifications and improvements of the Code, both in
wording and substance, were adopted. Here we only draw attention to
changes of some note. A full report on the Section’s decisions has been
published elsewhere (McNeill & al. in Taxon 54: 1057-1064. 2006).

Perhaps the most important single decision incorporated into the Vienna
Code was to deal with what many have recognized as a bomb waiting to
explode, the publication status of theses submitted for a higher degree. In
most, but certainly not all, countries, such theses have not traditionally
been considered media for effective publication under the Code, and de-
gree candidates have normally gone on to publish in journals or
monograph series the taxonomic novelties and nomenclatural actions con-
tained in their theses. However, as soon as theses ceased to be typewritten
with carbon copies, or as soon as they were made available commercially
by photo-reproduction, no provision existed in the Code to treat them as
other than effectively published. Because of the fact that in some other

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countries, notably the Netherlands and some Scandinavian countries, the-
ses, to be accepted, must be produced in substantial numbers and are
intended as effectively published media, it has not hitherto been possible
to resolve the issue. Nevertheless, despite the lack of any justification in
the Code for treating most theses produced over the past 40 years as other
than effectively published, the practice not to do so has persisted outside
of a few countries. In consequence, the Section took the unusual step of
accepting a retroactive change in the Code by deciding that no inde-
pendent non-serial publication stated to be a thesis submitted for a higher
degree on or after 1 January 1953 would be considered an effectively
published work without a statement to that effect or other internal evi-
dence. The Editorial Committee was instructed to provide examples of in-
ternal evidence that would best reflect current practice. The new Art. 30
Note 2 refers to the presence of an International Standard Book Number
(ISBN) or a statement of the name of the printer, publisher, or distributor
in the original printed version as such internal evidence.
 
 

Several proposals on criteria for valid publication of names were con-
sidered in Vienna. It was made explicit that names be composed only of
letters of the Latin alphabet except as otherwise provided in the Code, and
some clarification was accepted on what constitutes a description or diagn-
osis: statements on usage of plants, on cultural and cultivation features,
and on geographical origin or geological age are not acceptable, nor is the
mere mention of features but not their expression. Conceptually more sig-
nificant, however, was the decision to make provision for binding deci-
sions on whether or not a descriptive statement meets the requirement of
Art. 32.1(d) for a “description or diagnosis” – the so-called “nomina sub-
nuda” situation. This introduces into the Code an entirely new concept in
botanical nomenclature, although one that is well-established in zoolog-
ical nomenclature, namely rulings on interpretation of the Code itself.
Since the Sydney Congress of 1981, there has been provision for rulings
on whether or not two names or epithets are likely to be confused, and, of
course, in the conservation and rejection of names, judgement must be
made as to whether or not there will be “disadvantageous nomenclatural
change”, but these do not involve interpretation of the Code itself. The
procedure established is the same as that for judgement on whether names
or epithets are sufficiently alike to be confused (Art. 53.5) and the General
Committee will probably need to establish mechanisms to ensure that pro-
posed rulings coming from the different Permanent Committees are rea-
sonably consistent in their interpretation of Art. 32.1(d).

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Article 33, dealing with new combinations, although improved signifi-
cantly at the previous Congress, was again the subject of clarification,
principally in making a separation in the paragraphs of the Article be-
tween the situation before 1 January 1953 and the more precise require-
ments from that date onward. In addition it was made clearer that, prior to
1 January 1953, when the epithet of a previously and validly published
name that applies to the same taxon is adopted, the “presumed new com-
bination” is validly published if there is any indication at all of a basio-
nym, however indirect, but if there is no such indication, the new com-
bination is only validly published if it would otherwise be a validly pub-
lished name. By contrast, it was accepted in Vienna that on or after 1
January 1953 a claimed new combination or avowed substitute, that lacks
the full information required regarding the basionym or replaced synonym
is not validly published even though the name would otherwise be validly
published as the name of a new taxon. Although involving the somewhat
cumbersome expression “a generic name with a basionym” it has been
made explicit that most of the rules on combinations apply also to such
generic names.

Three important sets of changes were accepted in Vienna applying to
names in particular groups of organisms, fossil plants, pleomorphic fungi,
and fungi that had previously been named under the ICZN, respectively.

That for fossil plants was a reversal of one component of the rules on
morphotaxa introduced in the St Louis Code. At the St Louis Congress it
was argued (and accepted) that all fossil taxa should be treated as
morphotaxa. This has not, however, been considered appropriate by the
majority of palaeobotanists and a distinction between a morphotaxon and
a regular fossil taxon is now established. Whereas a morphotaxon com-
prises only the one part, life-history stage, or preservational state repre-
sented by the type of its name, any new fossil taxon that is described as
including more than one part, life-history stage, or preservational state is
not a morphotaxon. A corollary of this change is that Art. 11.7 of the Tok-
yo Code has had to be reinstated (as Art. 11.8 of the Vienna Code) be-
cause priority of a name of a taxon based on a non-fossil type competing
with one for the same taxon based on a fossil type is no longer implicit.
Opportunity has also been taken to make clear that later homonyms
are illegitimate whether the type is fossil or non-fossil.

The Code has long provided for a dual nomenclature for fungi with a
pleomorphic life history. Proposals to amend the article involved (Art. 59)
in order to facilitate a single name for a fungal taxon for which the

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anamorph-teleomorph relationship is known were extensively debated
amongst the mycologists present in Vienna who came to a consensus on
one very significant change in Art. 59, through which, by using the
epitype concept, a name, currently only applicable to an anamorph, may
be applied in the future to the whole organism (the holomorph) – cf. Art.
59.7.

A very important change in the Code, as it affects certain groups of
organisms now recognized as fungi, is the extension to fungi of the pro-
vision of the second sentence of Art. 45.4, previously applicable only to
algae. This deals with the names of taxa originally assigned to a group not
covered by the ICBN, but which are now considered to be either algae – or
now also fungi. To be accepted as validly published under the ICBN, such
names need only meet the requirements of the pertinent non-botanical
Code. The particular situation that triggered the proposal was that of the
Microsporidia, long considered protozoa and now recognized as fungi. In
addition, species names in the genus Pneumocystis (Archiascomycetes),
containing important human and other mammalian pathogens, none of
which were validly published under the St Louis Code (usually because of
the lack of a Latin diagnosis or description), are now also to be treated as
validly published. The change may have negative effects on a few names
in groups longer established as fungi such as slime moulds, labyrinthulids,
and trichomycetes, at least on authorship, but the numbers and importance
are considered small compared with the benefits for the microsporidians
and the species of Pneumocystis.

In the St Louis Code, the previously rather ambiguous restrictions on illus-
trations as types of names published after the type method entered the
Code were clarified by establishing that illustrations were permitted as
types of names published before 1 January 1958, but were prohibited
thereafter unless it were “impossible to preserve a specimen”, a condition
that many felt hard to define. Many at the Vienna Congress also felt that
this “clarification” had had the effect of retroactively devalidating names
published after 1957 with an illustration as type. The Congress agreed to
move the date and decided that for names of microscopic algae and
microfungi for which preservation of a type was technically difficult, the
type might be an illustration, but that for all other organisms, names pub-
lished on or after 1 January 2007 would require a specimen as type.

Stemming from the Report of the Special Committee on Suprageneric
Names set up at the St Louis Congress, it was agreed that the starting date
for valid publication of suprageneric names of spermatophytes, pterido-

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phytes, and bryophytes (excluding those mosses already with a 1801 start-
ing date) be 4 August 1789, the date of publication of Jussieu’s Genera
plantarum. This restores the original basis of spermatophyte family names
in App. IIB, dating to the Montreal Congress of 1959, which had never
been included in any article of the Code, and which had had to be changed
in the St Louis Code as a result of the Tokyo Congress failing to support a
proposal similar to this one and the St Louis Congress deleting a prot-
ecting footnote. The Section also established that parenthetic author cita-
tion is not permitted at suprageneric ranks.
 

Full details of unavoidable changes made to Appendix IIB since the St
Louis Code were published in the Second Report of the Special Commit-
tee on Suprageneric Names (Turland & Watson in Taxon 54: 491-499.
2005). The amendment to Art. 18.2, new Note 1 and voted Ex. 4, accepted
at the Vienna Congress, have necessitated some additional changes since
that Committee’s report and it is appropriate to detail these here. When, in
a work, taxa ranked as orders are subdivided into families, the names of
those taxa must be treated at the stated ranks and the orders cannot be
treated as having been published as families under Art. 18.2. The orders
and families in Berchtold & Presl’s O prirozenosti rostlin (1820) were al-
ready treated at the stated ranks, although Ambrosiaceae and Asteraceae,
previously listed from Martinov’s Tekhno-botanicheskii Slovar (1820)
have been updated because Berchtold & Presl published their book earlier
in 1820 (Jan-Apr) than Martinov (3 Aug) (A. Doweld, pers. comm.). In
Vines’s A student’s text-book of botany (1895) one order is subdivided in-
to families, two of which, Cymodoceaceae and Posidoniaceae, have been
updated. Six names in Link’s Handbuch, vols. 1 and 2 (1829) have been
updated because, in vol. 3, Link published two family names under the
order Fungi, which means that the names ranked as orders throughout the
work (Art. 35.5) must be treated as the names of orders, not as families as
has traditionally been done. The affected names are Dodonaeaceae, Meli-
anthaceae, Moraceae, Neuradaceae, Tetragoniaceae and Theophrasta-
ceae. In addition, Cordiaceae, which was updated to Link in the Special
Committee’s report, remains as listed in App. IIB in the St Louis Code.
Moreover, four family names previously overlooked in Berchtold &
Presl’s rare, later, multi-volume work of the same name (1823-1825) have
been updated: Aquifoliaceae, Cornaceae, Potamogetonaceae and Punica-
ceae.
 

The rules determining when a rank is denoted by a misplaced term (and
hence not validly published) were clarified and made more practical. This

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introduced the concepts of “minimum invalidity” (Art. 33.10), by which
only those names with rank-denoting terms that must be removed to pro-
vide the correct sequence would be considered not validly published, and
of “informal usage” (Art. 33.11), for situations in which the same term
was used for several different non-sequential ranks; such names are to be
treated as validly published but unranked. It was established that having
the ranks of both order and family in a work precluded application of Art.
18.2 (and similarly Art. 19.2 in the cases of suborder and subfamily), and
that sequential use of the same rank did not preclude valid publication
(Art. 33 Note 3).
 

One further date limit first appears in the Vienna Code. From 1 January
2007 a new combination, a new generic name with a basionym, or an
avowed substitute is not validly published unless its basionym or replaced
synonym is cited. Currently, although a full and direct reference to the
place of publication must be given, the basionym or replaced synonym
need only be indicated.
 

One portion of the Code that remains virtually unchanged after Vienna is
that for which by far the largest number of amendment proposals (147)
was submitted, namely orthography Of the 147 proposals, only five were
accepted but 107 were referred to the Editorial Committee. After review
of all these proposals by a subcommittee of the Editorial Committee (F. R.
Barrie, D. H. Nicolson, and N. J. Turland, who gratefully acknowledge
advice from R. Gereau, Missouri Botanical Garden), the changes incor-
porated into the Vienna Code are very few and none imposes a significant
change in practice. The most notable is a clarification of the respective ap-
plication of Rec. 60C.1 and 60C.2.
 

The Code establishes (Art. 12.1) that only if validly published does a
name have any status; indeed, unless otherwise indicated, the word
“name” in the Code means a name that has been validly published (Art.
6.3). For this reason recent editions of the Code have replaced “name” by
“designation” when the requirements for valid publication have not been
met, and the Vienna Code has taken this further by avoiding such contra-
dictory expressions as a name being validated, or being invalid. Given
the very different meaning of “valid” and “invalid” applied to names in
zoological nomenclature (equivalent to the botanical “correct” and “in-
correct”), it is convenient that neither “valid name” nor “invalid name”
need be used in botanical nomenclature: either a name is validly published
or else it is not a validly published name, i.e. not a name under the Code.

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The Vienna Code was prepared according to the procedures outlined in
Div. III, which have been operating with hardly any change since the Paris
Congress of 1954. A total of 312 individual numbered amendment pro-
posals were published in Taxon between February 2002 and November
2004. Their synopsis, with comments by the Rapporteurs, appeared in
Taxon (54: 215-250) in February 2005 and served as the basis for the
preliminary, non-binding mail vote by the members of the International
Association for Plant Taxonomy (and some other persons), as specified in
Division III of the Code. Tabulation of the mail vote was taken care of by
the Nomenclature Section’s Recorder, T. F. Stuessy and his assistants in
Vienna. The results were made available to the members of the Nomen-
clature Section at the beginning of its meetings; they were also tabulated
in the November 2005 issue of Taxon (54: 1057-1064), along with the
action taken by Congress.
 

The Nomenclature Section met at the Uni-Campus, University of Vienna,
Spitalgasse 2, Vienna, on 12-16 July 2005. With 198 registered members
carrying 402 institutional votes in addition to their personal votes, the
Vienna Section had a large attendance compared with many previous
Congresses but was substantially smaller than that at St Louis (with 297
members carrying 494 institutional votes). The Section Officers, previ-
ously appointed in conformity with Division III of the Code, were D. H.
Nicolson (President), T. F. Stuessy (Recorder), J. McNeill (Rapporteur-
général), and N. J. Turland (Vice-Rapporteur). Each Nomenclature Sec-
tion is entitled to define its own procedural rules within the limits set by
the Code, but tradition is held sacred. As on previous occasions, at least a
60% assenting majority was required for any proposed change to the Code
to be adopted. Proposals that received 75% or more “no” votes in the mail
ballot were ruled as rejected unless raised anew from the floor. The pro-
ceedings of the nomenclature sessions are presently being edited, based on
a tape transcript. They will be published later this year or early in 2007
in the serial Englera.
 

The Nomenclature Section also appointed the Editorial Committee for the
Vienna Code. As is traditional, only persons present at the Section meet-
ings were invited to serve on that Committee, which as the Code requires
is chaired by the Rapporteur-général and as is logical includes the Vice-
Rapporteur as its secretary. The Editorial Committee sadly lost one of its
members, when Guanghua Zhu died on 2 November 2005; the other 12
members of the committee convened on 6 January 2006 at the Missouri
Botanical Garden, St Louis, U.S.A., for a full week’s hard work. The

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Committee worked on the basis of a draft of the text of the main body of
the Code, prepared by the Chairman to incorporate the changes decided by
the Section, which was distributed by electronic mail in December 2005;
and of a preliminary version of the proceedings of the Section meetings,
as transcribed from tape and revised portion-wise by F. R. Barrie, D. L.
Hawksworth, J. McNeill, D. H Nicolson, and N. J. Turland.

Each Editorial Committee has the task of addressing matters specifically
referred to it, incorporating changes agreed by the Section, clarifying any
ambiguous wording, ensuring consistency, and providing additional ex-
amples for inclusion. The terms of the Committee’s mandate, as defined
by the Section in Vienna at its constituent meeting, included the usual
empowerment to alter the wording, the examples, or the location of Art-
icles and Recommendations, in so far as the meaning was not affected;
while retaining the present numbering in so far as possible.

The full Editorial Committee concentrated on the main body of the Code,
including Appendix I (hybrids). A new electronic draft of these portions
was completed prior to the end of its meeting, and provided to all Com-
mittee members for checking and for any further necessary clarification;
as a result a revised draft was prepared and circulated in mid-May to all
members for final proofreading. The contents of Appendices II-VI were
revised and updated in a bilateral process involving the Chairman and a
specialist for each of the groups concerned, normally a Committee mem-
ber (V. Demoulin for the fungi, D. H. Nicolson for genera and species of
vascular plants, P. C. Silva for the algae, J. E. Skog for fossil plants, N. J.
Turland for family names of vascular plants), except for the bryophytes
(G. Zijlstra, Utrecht, Secretary, Committee for Bryophyta, with assistance
from P. Isoviita, Helsinki). The Secretaries of the other Permanent Com-
mittees for particular groups provided useful assistance to the responsible
Editorial Committee member. The Subject index and the Index to scient-
ific names were revised by J. Prado; the Index to the Appendices was
updated by J. McNeill, who, with N. J. Turland, also cared for the final
copy-editing; the time-consuming task of final formatting and production
of camera-ready copy was carried out by N. J. Turland.

This is the proper place for us to thank all those who have contributed to
the publication of the new Code: our fellow members of the Editorial
Committee for their forbearance, helpfulness, and congeniality; all the
persons, just named, who contributed in a special way and much beyond
their normal commitment to particular editorial tasks; the botanists at
large who volunteered advice and suggestions, including relevant new

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examples; the International Association for Plant Taxonomy and its Sec-
retary, Tod Stuessy, for maintaining IAPT’s traditional commitment to
plant nomenclature by funding travel and some ancillary costs for the
Editorial Committee meeting in St Louis; the Missouri Botanical Garden
and its Director, Peter Raven, for providing accommodation free of charge
and hospitality for that meeting; and the publisher, Sven Koeltz, for his
helpfulness and the speed with which he once again guided the Code
through the printing process.

In addition to those who have helped to make possible this new edition of
the Code, botanical nomenclature depends on the scores of botanists who
serve on the Permanent Nomenclature Committees that work continuously
between Congresses, dealing principally with proposals for conservation
or rejection of names, and also those who are members of Special Com-
mittees set up by the Nomenclature Section of the Congress to review and
seek solutions to particular nomenclatural problems. Botanical nomen-
clature is remarkable for the large number of taxonomists who voluntarily
work so effectively and so extensively to the immeasurable benefit of all
those who use plant names. On their behalf we express our sincere thanks
to all who participate in this work.

The International Code of Botanical Nomenclature is published under the
ultimate authority of the International Botanical Congresses. Provisions
for the modification of the Code are detailed in Division III (p. 117). The
next International Botanical Congress will be held in Melbourne, Aus-
tralia from 23-30 July 2011, with a Nomenclature Section meeting likely
in the preceding week. Invitation for proposals to amend this Code and
instructions on procedure and format will be published in Taxon during
2007.

Like other international codes of nomenclature the ICBN has no legal sta-
tus and is dependent on the voluntary acceptance of its rules by authors,
editors, and other users of plant names. We trust that this Vienna Code
will make their work just that little easier.
 

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                       IMPORTANT DATES IN THE CODE
 

DATES UPON WHICH PARTICULAR PROVISIONS OF THE CODE

BECOME EFFECTIVE

ARTICLES INVOLVING DATES APPLICABLE TO THE MAIN

TAXONOMIC GROUPS

ARTICLES DEFINING THE DATES OF CERTAIN WORKS

Art. 13.1 (a-f), 13.5

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    International Code of Botanical Nomenclature, 2006  —  Vienna Code

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text: © 2006, IAPT  —  web-edition: © 2014, Paul van Rijckevorsel   (all rights reserved)

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