About the World Checklist of Vascular Plants

History

The World Checklist of Vascular Plants (WCVP) database was initiated in 1988 by Rafaël Govaerts and has now become an international collaborative programme with editors, compilers and reviewers from around the globe. The main aim of the checklists is to provide high quality expert reviewed taxonomic data on all vascular plants, building on the nomenclatural data provided by the International Plant Name Index (IPNI). The primary focus is the accepted species name as this is the single most important element necessary to communicate about plants and the key to biodiversity information. There has also been a considerable amount of data sharing with researchers and other online data providers who have incorporated large numbers of WCSP records. The data are also published on the GBIF checklist dataset, from where it is also incorporated as the main dataset of the Catalogue of Life Checklist. More recently it has become the default taxonomic backbone of World Flora Online (WFO) and we have been working closely with some of the Taxonomic Expert Networks (TEN) to use the WCVP data and platform as the basis for managing the taxonomic data of their TEN.

A full history and methodology can be found in the 2021 paper “The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity” published in Nature, Scientific Data:

https://www.nature.com/articles/s41597-021-00997-6

The WCVP database is updated daily and refreshed on Plants of the World Online (POWO) every Monday after the next Wednesday that an edit was made.

Apart from the name and taxonomic data, the database includes place and date of publication of all names are given. All data and downloads are standardised using standards set out by the Biodiversity Information Standards (TDWG). Citation of authors follows Authors of Plant Names (Brummitt & Powell, 1992); for book abbreviations, the standard is Taxonomic Literature, 2nd edn, or TL/2 for short (Stafleu & Cowan 1976-88; supplements, 1992-2000); and periodicals are abbreviated according to BPH-2 (Bridson, 2004). Names of nothospecies ('hybrids') and their synonyms are preceded by a multiplication sign.

Names

All names strictly follow the rules of the International Code of Nomenclature for algae, fungi, and plants (ICN). The orthography also strictly follows the rules as prescribed by the ICN. As the ICN follows the type method, the synonymy is based on the type of the name only, which may differ from the literature or common usage (so-called misapplied names). The ICN can be found on the IAPT website as well as its supplements, hosted by the Smithsonian.

Names and their associated nomenclatural data were primarily sourced from the International Plant Name Index (IPNI) or its predecessor Index Kewensis and subsequently standardized and edited. Newly published names are automatically added from IPNI to the database but are only made visible on the website after an editing and expert review phase of about one year. So remember that if you publish a name in November 2023, it will probably be entered into IPNI in the beginning of 2024 and may take until 2025 before it is fully edited and becomes visible on the POWO website.

Generic concepts

Acceptance of genera follows evolutionary classifications if the required new species combinations have been made and is primarily based on Plants of the World (Christenhusz & al., 2017). Recently published generic concepts covering the complete distributions of the taxa have generally been accepted. In particular, for Orchidaceae the generic concepts in Genera Orchidacearum (Pridgeon & al., 1999–2014) and subsequent updates by various authors that follow the guidelines below have been followed rather than a combination of independent partial and singular concepts, even if published more recently.

Unfortunately, we are not technically able to show accepted names using alternative taxonomies, although alternative classifications are covered though the references cited. When different generic classifications are proposed that represent monophyletic groups, then we accept the one that best fits the four guidelines (below) based on Bateman (2009) in an effort to divide the tree of life in a more consistent way.

Bateman (2009) proposed guidelines for how to construct a classification from a phylogenetic tree, which we try to implement for WCVP when alternative monophyletic generic concepts have been published. These guidelines attempt to provide a clear prioritisation with four explicit criteria, which are first explained in terms of properties that we wish a classification to incorporate and then the guidelines that are needed to adequately address these properties.

Property 1: A classification should consist only of natural (evolutionarily inclusive, well-circumscribed) groups.

Rule 1: Recognise only clearly monophyletic groups (clades).

Property 2: A classification has considerable stability when many data of the same or other kinds are gathered.

Rule 2: Preferably divide the tree at nodes that are relatively robust; the best evidence of robustness is provided by various measures of internal support (bootstrap or posterior probabilities).

Property 3: Each rank in a classification provides grouping information.

Rule 3: Minimise the number of nodes in a phylogenetic tree that simultaneously represent more than one taxonomic rank (most importantly, reduce the number of monospecific genera and other higher taxa comprising a single taxon). This redundancy is in some cases justified when such species are sister to a large clade composed of several genera, but not when embedded in a large clade and causes splitting of previous broader generic concepts.

Property 4: A proposed classification minimises changes to previous classifications.

Rule 4: Preferably divide the tree to minimise creation of (a) new names and (b) new combinations or replacement names.

Following these four guidelines helps to generate a robust, and biologically sound classification and dividing the tree of life in a more consistent way throughout WCVP. Inevitably, evolution will in some groups generate some clades in which morphological and molecular changes are uncoupled or incongruent (i.e., taxa for which molecular data provide clear results that are morphologically ambiguous and vice versa).

Species concepts

Acceptance of species and infraspecific taxa is based not only on assessments of literature and common practice but also, where possible, by reference to expert advice and (where necessary) to the herbarium or living collections. The general rule is that the latest published species level taxonomy and synonymy is followed within the accepted generic concepts. The checklist preferred view may however differ if (a) experts advise otherwise, (b) it is clear the most recent publication was not aware of the previous taxonomy (as it is e.g., not included in the bibliography) or (c) a more global authoritative publication is followed rather than a partial local one. Published historically different taxonomies are expressed in the references cited. A preferred view is however given as in most cases there is no current difference of opinion (at species level) and where there is disagreement (in our experience less than 1%) most users still prefer one unambiguous answer. For those specialists interested in the different opinions, those data are still available in the references cited and names listed.

Heterotypic synonyms without taxonomic references may often have received this synonymy from the original name data, which is mostly Index Kewensis vol. 1-2 or from large datasets that were incorporated like the Rosaceae database from Dr Pankhurst. For accepted taxa, the protologue is of course also a reference in which the name is accepted. Names may also be synonymised implicitly. If a name is not included in a revision of the group or geographical area to which it belongs, we implicitly conclude that the name is not accepted, and species names will therefore be listed as unplaced (see below) while infraspecific taxa are then normally synonymised with their higher taxon.

Infraspecific ranks

Infraspecific rank

If there is disagreement on the infraspecific rank at which a name should be accepted, the following key is used following Brummitt (1990) and Wood. & al. (2015):

1 Distribution range separate (so that non-overlapping rings can be drawn round them on a map) or nearly so, gene flow absent or very restricted between the infraspecific populations and differing in characters that are significant for taxonomic species differentiation within the genus........................................subsp.

1 Distribution ranges overlapping, gene flow possible and not differing in characters that are significant for taxonomic species differentiation within the genus........................................2.

2 Populations separate........................................var.

2 Mixed populations present........................................f.

Unplaced names

Unplaced names are names that cannot be accepted, nor can they be put into synonymy. This may be because the name is not validly published, or it is a later homonym and therefore illegitimate or because the genus name is not accepted. A name can also be unplaced because it cannot be put into synonymy which may be because (a) no correct name is available in an accepted genus, (b) no type material is known to exist and therefore it cannot be established to which species concept the name belongs, (c) the type material may be insufficient to establish a clear identity, (d) the type material may not have been studied by experts in the group and therefore no published synonymy exists.

From 2005 it became technically possible to add taxonomic references. As WCVP has a very diverse user group, both highly scientific botanical as well as mainstream horticultural publications are listed to reflect the broad usage of the names. All books that arrive at the library of the Royal Botanic Gardens, Kew and which can be found in its Library catalogue are screened as well as some 700 journals listed below and any other materials we receive from authors.

The primary importance of the references is to provide the evidence of which taxonomy is followed in WCVP. They also reflect current and historic alternative taxonomies. To get a full picture of the publications used for a particular species concept, it is important to keep in mind that the references express the published data only. This means that many homotypic and other synonyms do not have any references as an author may only publish that A is a synonym of B and not list all the homotypic synonyms of A. From this statement however, it can be logically concluded that all names homotypic with A must also be synonyms of B. Similarly, an author may publish that A is a synonym of B and another author that B is a synonym of C. The database will then logically show that A is a synonym of C even though no author may ever have explicitly published this. A name may also have been synonymised because the genus has been synonymised, even though not all or even none of the species synonymisations were explicitly published. Don’t forget that the protologue is also a reference in which the name is accepted. On the POWO website, the published source for a decision can be under “Publications”, where for accepted names, “POWO follows these authorities in accepting this name:" lists references we follow in accepting the name and "An alternative taxonomy had been proposed by the following authorities:" which list references that did not accept the name. For synonyms, “POWO follows these authorities in synonymising this name” lists references we follow in synonymising this name with, at the end of those references in square brackets, the accepted name used in that publication. Under “This name was accepted following an alternative taxonomy by these authorities” references are listed that accepted that name. By sorting the references on “Newest First” it will be easy to see the most recent publication followed by WCVP.

References

Bateman, R. (2009). Evolutionary classification of European orchids: the crucial importance of maximising explicit evidence and minimising authoritarian speculation. J. Eur. Orch., 41: 243 – 318.

Bridson, G., comp. & ed. (2004). Botanico-Periodicum-Huntianum/Second Edition. Pittsburgh: Hunt Institute for Botanical Documentation.
Brummitt, R. K. (1990). Species, subspecies, variety or form - an old problem revisited in tropical African Protea. Mitt. Inst. Allg. Bot. Hamburg. 23b: 677-682.
Brummitt, R. K. (2001). World Geographical Scheme for Recording Plant Distributions, ed 2. xvi, 138 pp. Hunt Institute for Botanical Documentation, Carnegie-Mellon University, Pittsburgh, Penna. (for the International Working Group on Taxonomic Databases for Plant Sciences). (Plant Taxonomic Database Standards, 2: version 1.0.) [ https://web.archive.org/web/20160125135239/http:/www.nhm.ac.uk/hosted_sites/tdwg/TDWG_geo2.pdf ]
Brummitt, R. K. & Powell, C. E., (1992). Authors of Plant Names. 732 pp. Kew: Royal Botanic Gardens. [ https://ipni.org/ ]
Christenhusz, M. J., Fay, M. F. & Chase, M. W. (2017) Plants Of The World: an Illustrated Encyclopedia of Vascular Plants. University of Chicago Press.

De Langhe, J. E. et al. (1983). Flora van België, het Groothertogdom Luxemburg, Noord-Frankrijk en de aangrenzende gebieden. civ, 970 pp., illus., map. Patrimonium, Nationale Plantentuin van België, Meise.
Farr, E. R., Leussink, J. A. & Zijlstra, G. (eds). (1986). Index Nominum Genericorum (Plantarum): Supplementum I. xv, 126 pp. Bohn, Scheltema & Holkema, The Hague. [ https://naturalhistory2.si.edu/botany/ing/ ]

Govaerts, R. (1995). World Checklist of Seed Plants, vol 1(1), 483 pp. MIM, Antwerp.

Govaerts, R., Nic Lughadha, E., Black, N., Turner, R. & Paton, A. (2021). The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity. https://doi.org/10.1038/s41597-021-00997-6 Scientific Data 8: 215.
Raunkiær, C. (1934). The Life Forms of Plants and Statistical Plant Geography. xvi, 632 pp., illus. Oxford University Press, London.
Stafleu, F. & Cowan, R. S. (1976-88). Taxonomic Literature: A Selective Guide to Botanical Publications and Collections with Dates, Commentaries and Types. 2nd edn. 7 vols. Utrecht: Bohn, Scheltema & Holkema. (Regnum Vegetabilie 94, 98, 105, 110, 112, 115, 116.) Continued as Stafleu, F. et al.. (1992-2000). Taxonomic Literature, Supplement. Vols. 1-6. Koenigstein, Germany: Koeltz. (Regnum Vegetabile 125, passim. As of 2000 six volumes published.)[ https://www.biodiversitylibrary.org/bibliography/48631 ]

Wood, J.R.I., Williams, B.R.M., Mitchell, T.C., Carine, M.A., Harris, D.J. & Scotland, R.W. (2015). A foundation monograph of Convolvulus (Convolvulaceae). PhytoKeys 51: 19. [ https://doi.org/10.3897/phytokeys.51.7104 ]

List of Journals screened up to the end of 2023.

Geographical Distribution

Native and introduced wild distributions of accepted taxa are furnished in two ways: firstly by a generalised statement in narrative form, and secondly as TDWG geographical codes (Brummitt, 2001) expressed to that system's third level. Examples of the former include:

• Texas to C. America
• Mexico (Veracruz)
• Europe to Iran
• E. Himalaya, Tibet, China (W. Yunnan)
• Philippines (Luzon)
• S. Trop. America

Native distribution are areas where the plants have been present since before the last Ice Age or arrived by natural colonisation. Introduced distributions are areas where plants were introduced accidentally or deliberately by humans, which includes archaeophytes, neophytes, alien, casual, invasive and naturalised plants but not cultivated ones or those merely planted in wild areas but not self-reproducing. Hybrids that occur naturally between introduced or native and introduced plants are also classified as “introduced”. When the presence of a taxon in a given region or location is not certainly known, a question mark is used, e.g. New Ireland ?; when an exact location within a country is not known, a question mark within brackets is used, e.g. Mexico (?). Distributions of genera are furnished in a relatively simplified form, any endemic regions being given within brackets.

With respect to the TDWG codes, the region is indicated by the two-digit number (representative of the first two levels), the first digit also indicating the continent. The letter codes following the digits, when given, represent the third-level unit (a country, state or other comparable area). They usually are the first three letters of a given unit's name, but sometimes are contractions. When pointing to a particular code, the complete name will be provided. If the country code is not known, '+' is used. For taxa that are known or appear to be extinct in a given region, '†' is used after the country code. Non-native status is expressed by putting the third-level codes in lower case and, if in a second-level region all occurrences are the result of naturalisation, the code number for the region is placed in brackets. The application of question marks is as indicated above for geographical regions. Examples include:

• 12 SPA [SW. Europe: Spain]
• 32 + [C. Asia (more exact distribution not known)]
• 36 CHN? 38 JAP KOR [Doubtful in China North Central, Eastern Asia; Japan and Korea]
• 51 NZN NZS [New Zealand: North and South Islands]
• (76) ari 77 NWM TEX [SC. U.S.A., naturalized in Arizona]
• 77 TEX† [SC. U.S.A.: Texas, where extinct]

Life-forms

The terminology for life-forms, definitions of which follow, is based on the system of Raunkiær (1934, especially chapters 1 and 2) with modifications derived from Flora van België, het Groothertogdom Luxemburg, Noord-Frankrijk en aangrenzende gebieden (De Langhe et al. 1983: pp. xvii-xviii, 869 (fig. 16)). Many plant families have their own particular lifeforms. It is therefore only attempted to give a very broad and general lifeform, mainly to aid global searches over different groups. On the POWO website, only the English forms are shown.

Main Categories:

phanerophyte (phan.) tree
stems: woody and persisting for several years
buds: normally above 3 m
e.g.: small and large trees

herbaceous phanerophyte (herb. phan.) herbaceous tree
stems: herbaceous and persisting for several years
buds: above soil-level
e.g.: Musa balbisiana

nanophanerophyte (nanophan.) shrub
stems: woody and persisting for several years
buds: above soil level but normally below 3 m
e.g.: shrubs

chamaephyte (cham.) subshrub
stems: herbaceous and/or woody and persisting for several years
buds: on or just above soil level, never above 50 cm
e.g.: Alyssum, Acaena, Acantholimon, Saxifraga

hemicryptophyte (hemicr.) perennial
stems: herbaceous, often dying back after the growing season, with shoots
at soil level surviving
buds: just on or below soil level
e.g.: Aster, Viola odorata

geophyte; plants with underground storage organs
hemicryptophytes that survive unfavourable seasons in the form of a rhizome, bulb, tuber or rootbud.
The term tuber is used here in a broad sense and includes every storage organ that is not a rhizome, bulb or rootbud.

helophyte (hel.) perennial marsh plant
hemicryptophytes that grow in soil saturated with water or in water. leaf and flower
bearing shoots rise above water
e.g.: Typha, Echinodorus

hydrophyte; aquatic plants
stems: vegetative shoots sunk in water
buds: permanently or temporarily on the bottom of the water

hydrohemicryptophyte (hydrohemicr.)
e.g. Stratioides

hydrogeophyte
e.g. Nymphaea, Nuphar

hydrotherophyte (hydrother.)
e.g. Lemna, Utricularia vulgaris

therophyte (ther.) annual
plants that survive unfavourable seasons in the form of seeds and complete their life-history during the favorable season.
e.g. annuals

Others

bamboo
biennial
pseudobulb
pachycaul
cereiform
cauduciform

Additional information

climbing (cl.)
e.g.: cl. phan.: Hedera helix
cl. nanophan.: Clematis florida
cl. hemicr.: Vicia cracca
cl. tuber geophyte: Tropaeolum tuberosum
cl. ther.: Pisum sativum
(cl.) nanophan: for plants that are sometimes climbing
succulent (succ.)
e.g.: succ. nanophan.: Opuntia ficus-indica
succ. cham.: Lophophora williamsii
succ. ther.: Sedum azureum
cl. succ. nanophan.: Cissus quadrangula

epiphytic and lithophytic
Growing on trees or rocks, without extracting nutrition from the host.

parasitic (par.)
hemiparasitic (hemipar.)
parasitic plants that are still able to photosynthesise
e.g. Viscum album is a hemipar. nanophan.
holoparasitic (holopar.)
parasitic plants that are fully dependent on their host
e.g. Orobanche ramosa is a holopar. ther.

holomycotroph (often incorrectly called saprophyte)
e.g. Neottia nidus-avis is holomycotroph.

Abbreviations used