Introduction

Our aim is to provide a detailed global biogeographical regionalisation (i.e. hierarchical classification) for the world’s terrestrial biota to the subregion level. Our study will advance the scheme of Morrone (2015a) by using a thorough biogeographical classification or area taxonomy (see Ebach and Michaux 2017) to justify each area as well as using the International Code of Area Nomenclature (ICAN; Ebach et al. 2008) to stabilise the proliferation of names by providing a synonymy, diagnosis and discussion for each valid name. Names within the biogeographical hierarchy usually fall into five levels, namely kingdoms (also known as realms), regions, dominions, provinces and districts. In some cases subkingdoms, subregions or subprovinces are recognised. The resulting hierarchical area taxonomy may be used as the basis for future global, intercontinental or regional biogeographic studies, without the need to apply new names. This study does not propose how to discover or identify natural biogeographic areas (i.e. endemic areas), rather we use the biogeographical literature to build a database of available names with a list of synonymies within a biogeographical hierarchy called an area taxonomy. We hope our study builds towards a global standard and database for biogeographic areas and names.

To understand the vast biogeographical literature and past discussions concerning the validity of certain areas, such as the Holarctic, a historical excerpt is presented below. For a full account, we recommend von Hofsten (1916) for early history of biogeography, Egerton (2012) for the history of ecological biogeography, Wallaschek (2009, 2010a, 2010b, 2011a, 2011b, 2012a, 2012b, 2012c, 2013a, 2013b, 2014, 2015a, 2015b) for the history of zoogeography, and Ebach (2015) for the history of 18th and 19th century regionalisation. The summary focuses on past controversies, including the description of natural regions and the acceptance of the Holarctic in the 19th, 20th and 21st centuries.

Summary of the history of biogeographical regionalisation

Global bioregionalisations were first proposed in the early 19th century, most notably by de Candolle (1805, 1820), Latreille (1815), Schouw (1823), Prichard (1826) and Swainson (1835). The first global hierarchical area classification was proposed by Wagner (1844, 1845, 1846a, 1846b) in a three-part monograph titled Die Geographische Verbreitung der Säugethiere Dargestellt [The geographical distribution of mammals], which was based on the mammalian distributions proposed by Illiger (1815; see also von Hofsten 1916; Kendeigh 1954; Smith 2005; Egerton 2012; Wallaschek 2015a; Ebach 2021). Wagner’s work contained the first global biogeographic map and area taxonomy (map republished in Hermogenes de Mendonça and Ebach 2020; area taxonomy republished in Ebach 2021; Fig. 1, Table 1). Unlike previous maps, such as Schouw’s Verbreitungsbezirk und Vertheilungsweise der Arten [Distributional areas and distributions of species] (Schouw 1823), Wagner’s map included all terrestrial areas rather than the distribution of economically important cereal crops (e.g. oats, wheat, maize, rice, rye). The map it most closely resembles is Zimmermann’s Tabula mundi geographico zoologica sistens quadrupedes: hucusque notos sedibus suis adscriptos [Geographical map of the world’s quadrupeds] (Zimmermann 1777, p. 1783; Fig. 2); however, Zimmermann’s map simply shows the distributions of terrestrial quadrupeds over a map of the Old and New Worlds (i.e. North and South America, Africa, Europe, Asia and Australia). Wagner’s map attempted to show the actual distributional areas of mammals as a whole. Wagner had created the first global biogeographic map that represented the first hierarchical classification (Table 1).

Fig. 1.

Representation of the distribution of mammals according to their zones and provinces by Wagner (1844). The southern boundary of the northern polar province is indicated by a line of a different colour, drawn somewhat further south than the equatorial border of the Arctic fox ([Vulpes] lagopus), although not so far in some places as the reindeer may descend there on their summer migrations. The southern polar province is not included in this map, because it is only in the process of discovery and, according to all previous experience, it does not harbour land mammals (Wagner 1846b, p. 241; Table 1).

Table 1.

The hierarchical classification of zones, provinces, subprovinces and regions listed by Wagner (1844, 1845, 1846a, 1846b).

Fig. 2.

Tabula mundi geographico zoologica sistens quadrupedes hucusque notos sedibus suis adscriptos, second edition (Zimmermann 1783). The revised map in the 1783 German edition contains the newly discovered Sandwich Islands (Hawai’i) and the Seychelles, which were absent in the original 1777 edition (Ebach 2015, p. 31; source: National Library of Australia).

Natural areas

Prior to Wagner, there was much discussion among zoogeographers over the ‘naturalness’ of areas. Early naturalists, such as Fabricius (1778) and Latreille (1815), had proposed areas that Swainson (1835) had considered to be artificial. In fact, Kirby and Spence (1826) stated:

Yet, this is exactly what phytogeographers such as Schouw (1823), Meyen (1846) and Grisebach (1872) and later zoogeographers (e.g. Forbes 1846; Schmarda 1853; Merriam 1892) were practising during the 19th century, a method that continues to this day (see Olson et al. 2001).

This approach differs from the identification of natural areas, that is, the earth being divided into naturally occurring biogeographical units on the basis of their endemic taxa, in the same way the living world is divided into taxa (e.g. species, genera, families). A world naturally divided into units would also apply at the biotic level; Australia has a unique flora and fauna, that is, a biota, which is very different from the biota of other continents with similar climates. Yet, when we observe this biota, we discover that plant species interact with the landscape (i.e. topography, soil, climate) and, therefore, produce plant forms and vegetation types. For example, an arid area will not produce the same types of trees you find in say, a rainforest. The plant forms in an arid area are stunted, have small leaves, where rainforest plants would be taller, form canopies and have larger leaves. The whole vegetation in fact would be different. A rainforest would have dense foliage, high trees all competing for sunlight, where an arid area would have a vegetation type that suits the dry and hot environment that it grows in.

Both approaches, the taxonomic and vegetational, can be described as ‘natural’; the taxonomic is a result of biogeographical homology and the vegetational is a result of plant forms. Yet, only the taxonomic is in anyway evolutionary in the simplest sense of the word. If we say that the family Macropodidae, namely the kangaroos and their allies, is endemic to Australasia, then we mean that kangaroos and all their nearest relatives are more closely related to each other (a monophyletic or natural taxon) than they are to anything else; that is, they are endemic to one area. With vegetation, this becomes problematic. A rainforest may be defined in a particular way, on the basis of the types of unique plant forms, rainfall, soil type and so on. This means that there is a universal rainforest, but the taxa that inhabit one rainforest may share only a distant relationship with the taxa in another. In this sense the plant forms and vegetation appear to be natural, but from an evolutionary standpoint they are artificial groups. The difference between taxonomic and vegetational regionalisations jarred with early ecologists such as Cowles (1908), who chastised taxonomy for producing artificial species, believing that taxonomists should be concerned with populations and their physiological forms, given that it is the environment that controls these forms.

Hierarchical area taxonomy

For the practical purposes of area taxonomy (i.e. biogeographical regionalisation, bioregionalisation, area classification), how one determines an area is not critical. Rather, it is how these areas relate that determines naturalness, and that relationship is based on biogeographical homology (Morrone 2001a; Ebach and Michaux 2017). Sclater (1858) hinted at this relationship being vital:

A decade later, Huxley (1868) made a similar statement on relationship:

Yet, few 19th century plant and animal geographers tried to uncover natural biotic relationships. The biogeographic map produced by de Candolle (1805) attempted to use soils, climate and drainage to justify a relationship or connection, but failed. The link between biotic relationships and biogeographic areas came much later in the 20th century (Platnick and Nelson 1978; Rosen 1979; Nelson and Platnick 1981; Nelson and Ladiges 1996).

Sclater (1858) did provide a method to determine potential ‘natural’ areas by measuring endemicity and tallying the number of endemic bird taxa in each area. Essentially, Sclater’s areas were hierarchical in nature and covered all territorial areas, with the exception of the newly explored Antarctica and Subantarctic Islands. Sclater’s areas and his methodology of tallying up the numbers of taxa endemic to each area were adopted by Wallace (1876a, 1876b), who recognised Sclater’s six avian zoogeographic regions based on vertebrate distributions (Fig. 3, Table 2). Wallace preferred Sclater’s system because it initiated:

Fig. 3.

Zoogeographic regions recognised by Wallace (1876a, 1876b) in The Geographical Distribution of Animals.

Table 2.

The Sclater–Wallacean areas based on vertebrate distributions.

But not all of Sclater’s areas were adopted:

Wallace’s biggest problem was the push back from other vertebrate zoologists, such as Heilprin (1882) and Allen (1871), who regarded the circumpolar zones as valid climatic areas based on a law of the distribution of life in circumpolar zones, which was addressed in some detail by Wallace (1876a):

Wallace here conjures up the stations and habitations of de Candolle (1820):

Allen states:

Other zoogeographers adopted the Holarctic including Blanford (1890), who used the term Aquilonian as an equivalent, and Lydekker (1896; see Arldt 1906 for further authors). The debate between Wallace and his adoptees (i.e. Sharpe 1893; Sclater and Sclater 1899; Fig. 4, 5) and North American zoologists such as Allen, Heilprin, Gill, Günther and Cope (neither of whom published a map) continued in society journals (see Ebach 2015). English ornithologist Alfred Newton, friend to both sides, tried to convince Wallace of the reality of a Holarctic by private correspondence shortly before the publication of the The Geographical Distribution of Animals (Wallace 1876a, 1876b):

Fig. 4.

Zoogeographical areas illustrating the Distributions of Birds by R. Bowlder Sharpe (1893). The classification is loyal to Wallace (1876a, 1876b) because it clearly distinguishes the Nearctic from the Palaearctic.

Fig. 5.

Outline map of the world, showing the six regions of the geographical distribution of mammals (Sclater and Sclater 1899, map opposite p. 16).

Wallace was not persuaded by Newton’s argument and, by 1882, the argument has spilled over into the pages of Nature (see Ebach 2015):

Others retained Wallace’s usage for purely nomenclatural reasons:

Sclater (1897) and later in their Geography of Mammals father and son Sclater and Sclater (1899) sided with Wallace for the simple reason that the Nearctic and Palearctic represented two distinct faunas:

Given this heated debate, are both sides talking past each other? If we look back to Sclater (1858), we find that his creations Neogeana and Palæogeana are based on the notion that the regions of the New World, for instance, share a closer relationship to each other than they do to the regions of the Old World and vice versa:

It is through classification, rather than through any distributional ‘laws’ that Sclater viewed zoogeography; after all, he firmly believed that each World was created by God (hence ‘creatio’). The notion that any distributional laws were in effect was never entertained. Wallace carried on this notion of relationship by tabling the world’s areas on the basis of vertebrates (Table 2). By placing the Australian and Neotropical regions into Notogea, he assumed relationship and not distributional laws. The idea that distributional laws shape area classification was introduced by the American zoogeographers who were more influenced by the proto-ecological ideas of the Humboldtians, who decided that the environment had a greater part to play in determining distribution. Again, here we see the division between those who see taxonomic distributions as natural versus those who feel that naturalness is something environmental. Nelson (1978) attempted to separate out these two practitioners into historical and ecological biogeographers, on the basis of the stations and habitations divide of de Candolle (1820).

One may wonder whether the Holarctic is the first major ecological zoogeographical region ever proposed. If so, it runs contrary to the Sclater–Wallacean or historical theme of natural areas based on endemicity, rather than on distributional ‘laws’.

The final word on 19th century zoogeographical regionalisation is that of Bartholomew et al. (1911). In their colourfully illustrated Physical Atlas, they redrew the published maps of Sclater (1858, 1897), Wallace (1876a, 1876b), Heilprin (1887), Lydekker (1896), Ortmann (1896) and Sclater and Sclater (1899). Bartholomew et al. (1911) admitted that:

The short account of Bartholomew et al. (1911) starts with Sclater (1858) and ends with Sclater and Sclater (1899). Bartholomew et al. (1911) adopted the area classification of Wallace (1876a, 1876b), which is reiterated in Beddard (1895), a work that they describe as presenting ‘the subject in a different light from any of its predecessors’. Why Bartholomew et al. (1911) thought Beddard (1895) was any different to say Sclater and Sclater (1899) is unclear, as Beddard has adopted Wallace’s areas without any reference to the Holarctic. The wholesale disregard of the Holarctic is unusual, given that Wallace’s own Arctogæa incorporates the Nearctic and Palearctic.

In the spirit of Sclater and Wallace, we view the Holarctic as nothing more than a higher level area (a division of a larger area perhaps) that groups two regions on the basis of the notion of relatedness; that is, the Nearctic and the Palearctic share a greater relationship on the basis of the taxa they share, than to any other region. Yet, the adoption of the Holarctic, especially by zoologists, had taken much longer, with similar debates about its validity appearing in the early part of the 21st century (e.g. Escalante 2017), whereas others simply ignored it as a possible relationship among larger areas (e.g. Holt et al. 2013a, 2013b).

Adoption of Wallace’s areas by phytogeographers

Until the late 19th century, zoo- and phytogeography adopted separate classifications. For example, Engler (1882) divided the world’s flora into five main areas, namely the Northern and Southern Extratropical kingdoms, the Palaeotropical kingdom of the Old World, and the South American and Old Oceanic kingdoms (Fig. 6). Engler (1882) placed the Arctic region within the Northern Extratropical kingdom, an area resembling the Holotropical kingdom. Engler (1899) slightly altered the names and placed them all into the following five kingdoms: Northern Extratropical or Boreal, Palaeotropical, Central and South American, Austral (Old Oceanic) and Oceanic. The last kingdom was missing in the scheme of Engler (1882). Arldt (1907, map 1) used the same term ‘Arctic region’ to describe his circumpolar area in his Biogeographic Classification of the Continents (Fig. 7), which he classified as the Känogäisches kingdom, which includes the Holarctic region and three subregions, the Palearctic, Boreal and Nearctic. Arldt’s classification is unique, because it is based on terrestrial, freshwater, marine plant and animal distributions as well as the work of both zoo- and phytogeographers. His classification maybe seen as a review and an amalgam of 19th century plant and animal geography. Unfortunately, Arldt’s work is often overlooked in the history of biogeography (see Dowding and Ebach 2018), even though his own biogeographic classification looks incredibly modern by comparison to other early 20th century plant and animal geographers. In any case, Arldt (1907) preserved all of the Sclater–Wallacean regions as well as incorporating those of Heilprin (i.e. Holarctic) and Engler (i.e. Arctic) and served as a great revisionary work for 19th century biogeography.

Fig. 6.

Verteilung der wichtigsten physiologischen Pflanzengruppen in den Vegetationsgebieten der Erde [Division of the important physiological plant groups in the vegetation of the earth] (Engler 1882, p. 387).

Fig. 7.

Biogeographische Gliederung der Kontinente [Biogeographic Classification of the Continents] (Arldt 1907, map 1). Shaded areas indicate regions; hatched lines indicate the boundaries of kingdoms; bold lines the boundaries of regions; and thin lines the boundaries of subregions.

Another work on global phytogeography is Good (1947, 1963; Fig. 8), who noted that:

Fig. 8.

Map of the world showing Good’s floristic regions (Good 1963, plate 4).

Good (1947, 1963) simplified Engler’s classification system in his Geography of Flowering Plants, designating six floristic kingdoms, namely Boreal [sensu Holarctic], Paleotropical, Neotropical, South African, Australian and Antarctic (Table 2). Good continued:

The other floristic classification scheme by Takhtajan (1978, 1986; Fig. 9) seemingly solidified phytogeography in the minds of 20th and 21st century biogeographers. Takhtajan reintroduced the Holarctic as a kingdom, converted Good’s Boreal kingdom into a subkingdom, and renamed Good’s South African and Antarctic kingdoms into the Cape and Holantarctic kingdoms respectively (Table 3). Takhtajan’s system may seem like Engler’s (1882, 1908); however, it does incorporate Heilprin’s Holarctic and several of the Sclater–Wallacean regions (Table 3), which were absent in previous floristic schemes (Engler 1882, 1899).

Fig. 9.

Takhtajan’s floristic kingdoms and regions of the earth (Takhtajan 1978, separate map). Red solid and dashed lines indicate the boundaries of kingdoms; green solid and dashed lines indicate the boundaries of the regions.

Table 3.

Classifications of Wallace (1876a, 1876b), Engler (1882), Good (1947) and Takhtajan (1978, 1986) compared.

Later 20th and 21st century global biogeographic regionalisations

Global regionalisation after 1946 follows a similar theme of that of later 19th century area classification, including how to reconcile the Holarctic with the Nearctic and Palaearctic regions. Late 20th and 21st century biogeographical regionalisation may be divided into the following three groups: those who, knowingly or unknowingly, rejected the Holarctic in favour of the Nearctic and Palearctic (Udvardy 1975; Smith 1983; Kreft and Jetz 2010; Procheş and Ramdhani 2012; Holt et al. 2013a, 2013b; Rueda et al. 2013); those who accepted only a unified Holarctic (e.g. Schmidt 1954; de Lattin 1967; Rapoport 1968; Müller 1986; Cox 2001); and those who attempted to incorporate each under a larger division (Darlington 1957; Poynton 1959; Lopatin 1980; Morrone 2002, 2015a). Other problems raised in generating classification were the inclusion of New Zealand into the Antarctic or Holantarctic kingdom (i.e. Udvardy 1975), and whether to include or not transition zones (see Hermogenes de Mendonça and Ebach 2020 for a recent review).

Establishment of the Holarctic as a unified biogeographic area

The arguments for retaining the Holarctic are numerous. Darlington (1957) recognised six regions grouped into the following three kingdoms: Megagea (Ethiopian, Indomalayan, Palearctic and Nearctic regions), Neogea (Neotropical region) and Notogea (Australian region). Rather than choosing one classification over another, Darlington diplomatically noted:

If animals are Holarctic because they occur in both northern temperate zones, why not create a higher area ‘Holarctic’ in which the Nearctic and Palearctic are classified as subregions, as proposed earlier by Schmidt (1954) and Hershkovitz (1958)? Earlier 20th century zoogeographical classifications had included the Holarctic, with the Palaearctic and Nearctic as subareas, including Nichols (1943), who divided the freshwater fish fauna into ‘II. Continental: 1. Northern: A. Holarctic, a. Palaearctic and, b. Nearctic’ (Nichols 1943, p. 3); and Bobrinskiy et al. (1946), who placed the Holarctic region within Arctogea (see Beron 2018, p. 906). Herschkovitz noted that:

Poynton (1959), referring to Hershkovitz (1958), classified the Nearctic and Palearctic as subregions within a larger Holarctic region (Fig. 10), although without referring to Schmidt (1954).

Fig. 10.

Simplified diagram of the main conventional zoogeographical subdivisions (Poynton 1959, fig. 1). The Palaearctic and Nearctic are treated as subregions within a larger Holarctic region.

Whereas the Holarctic was accepted by mammalogists (e.g. Hershkovitz) and herpetologists (e.g. Schmidt), entomologists were less convinced. German entomologist Gustav de Lattin in his Grundriß der Zoogeographie (de Lattin 1967) was one of the few to recognise the challenge, and formalised the Holarctic as a zoogeographic area, with the Palearctic and Nearctic as subregions (see Beron 2018), in what Illies called:

Illies’ (1968) reference to Darlington is remarkable, given the number of already existing studies that accepted the Holarctic.

The acceptance of the Holarctic as a major area, which represents the Nearctic and Palearctic in their entirety or as subregions, was common in the second half of the 20th century. Rapoport (1968) proposed a biogeographic division of the earth into three regions or ‘biogeographic belts’, named Holarctic, Holotropical and Holantarctic (Fig. 11). Müller (1986) recognised nine divisions grouped into the following five kingdoms: Holarctic (Nearctic and Palearctic regions), Paleotropical (Ethiopian, Madagascan and Oriental regions), Australian (Australian, Oceanic, New Zealand and Hawaiian regions), Neotropical (Neotropical region) and Archinotic (Archinotic region). Bǎnǎrescu (1975) also recognised the Holarctic as a freshwater region, but not the Nearctic or Palearctic regions. Lopatin (1980) recognised the Arctogean kingdom containing the Palearctic and Nearctic regions, possibly because of the seniority of the name (Wallace 1876a, 1876b) to the later Holarctic (Heilprin 1882). The acceptance of the Holarctic continued into the late 20th and early 21st centuries. For example, Morrone (2002, 2015a) recognised the Holarctic as a kingdom and the Nearctic and Palearctic as its regions. Yet, the rejection of the Holarctic as a relational region began with the quantification of bioregionalisation.

Fig. 11.

Biogeographic regionalisation of Rapoport (1968) recognising the Holarctic, Holotropical and Holantarctic belts.

Quantification of areas and the fate of the Holarctic

With the development of faster computer algorithms and the emergence of distributional databases, bioregionalisation entered a quantitative phase by the early 2000s. Early studies on global bioregionalisation included analyses using the distributional data of conifers (Sneath 1967), mammals (Smith 1983), Liliiforae (Conran 1995) and bumble-bees (Williams 1996). Both Sneath (1967) and Smith (1983) recovered the Holarctic, whereas the analyses by Conran (1995) and Williams (1996) did not.

Further bioregionalisation analyses based on bat (Procheş 2005) and gymnosperm distributions (Procheş 2006) found the Palearctic and Nearctic, but little similarity between them (i.e. they are more similar to other areas than to each other). The trend between recovering and not recovering the Holarctic continued with studies in the 2010s. In an analysis using vertebrate distributional data, Procheş and Ramdhani (2012) recovered both the Nearctic and Palearctic but failed to recover the Holarctic. They did admit, however, that using:

Rueda et al. (2013) recovered regions similar to those of Wallace (1876a, 1876b), using amphibian, bird and mammal data, and Escalante (2017) recovered Wallace’s Australian, Ethiopian, Neotropical, and Oriental regions by using mammal data. Neither study found evidence for the Holarctic.

Two studies that recovered the Holarctic were those of Kreft and Jetz (2010; Fig. 12), which used mammal distributional data, and Holt et al. (2013a, 2013b; Fig. 13), which used vertebrate data. The analysis of Kreft and Jetz (2010) found the Nearctic and Palearctic to have a greater similarity to each other, thereby justifying a Holarctic at the level of species, genus and family of volant and non-volant taxa (Kreft and Jetz 2010; Fig. 6). The analysis of Holt et al. (2013a) failed to mention the significance of their findings. Tucked away in the appendices is a dendrogram ‘of cross-taxon zoogeographic realms based on phyla-distributional data for amphibian, bird and non-marine mammal species of the world’ (Holt et al. 2013a, fig. S1), which shows the phylogenetic β diversity values between the Nearctic and Palearctic to justify a Holarctic kingdom; yet, the term was not used in the paper or in the appendices.

Fig. 12.

The six major biogeographical divisions of Kreft and Jetz (2010) are highlighted in the dendrogram with large coloured rectangles: Australian (orange); Neotropical (red); African (brown); Oriental (yellow); Palaearctic (blue); Nearctic (green). The first 30 groups in the dendrogram (small rectangles) and in the map are displayed in different colours. Additionally, the first 60 groups are indicated with black boundaries in the map (Kreft and Jetz 2010, fig 9).

Fig. 13.

Map of the terrestrial zoogeographic realms and regions of the world (Holt et al. 2013a, fig. 1).

The usage of the Holarctic is justified both historically and quantitatively. Most quantitative studies have recovered the Holarctic, and, in doing so, the Holotropical. Given this long tradition that extends back to Heilprin (1882), we feel confident that future studies will recover the Holarctic, and by definition the Holotropical. A recent quantitative study using plant data did, indeed, recover three clusters that correspond strongly to the Holarctic, Austral and Holotropical.

Towards a terrestrial biogeographical regionalisation of the world

The biogeographical regionalisation presented below divides the world into three kingdoms, following Newbigin (1950), Kuschel (1963), Rapoport (1968), Morrone (2002, 2015a), Moreira-Muñoz (2007) and Carta et al. (2022). Within these kingdoms, we recognise 2 subkingdoms, 8 regions, 21 subregions and 5 transition zones (Fig. 14, Table 4). This interim global biogeographic classification to the subregion level takes into account all previous classifications and names within a formal nomenclatural synonymy that follows the ICAN (Ebach et al. 2008; and see below). Each list of synonymies is followed by a diagnosis and a list of regions. The name of each region is followed by a list of synonymies, a diagnosis and remarks. Within each region, the proposed subregions are provided, although we note that some of them, particularly in the Palearctic, Ethiopian and Oriental regions, still need analysis. In the areas of overlap between regions belonging to different kingdoms, five transition zones are delimited, as formerly recognised by several authors (e.g. Müller 1986; Halffter 1987; Morrone 2006, 2014, 2015a, 2015b; Kreft and Jetz 2013). No new names are proposed in this study.

Fig. 14.

World biogeographical regionalisation, with indication of the regions and transition zones. (1) Nearctic region; (2) Palearctic region; (3) Neotropical region; (4) Ethiopian region; (5) Oriental region; (6) Andean region; (7) Australian region; (8) Antarctic region; (9) Mexican transition zone; (10) Chinese transition zone; (11) Saharo-Arabian transition zone; (12) South American transition zone; (13) Indo-Malayan transition zone.

Table 4.

The terrestrial kingdoms, subkingdoms, regions, subregions and transition zones of the world recognised herein.

The naming system within this and other biogeographic classifications follows the ICAN (Ebach et al. 2008). The ICAN was proposed so as to stem the flow of area names and to formalise a practise, so that one diagnosed area is assigned a single name. A biogeographical nomenclature as proposed by Wallace (1894) did not question:

In other words, nomenclature, that is how biogeographers name areas, is not part of the discovery process of biogeography, but rather a convenient way to organise names without confusion. We may draw an analogy to the Botanical and Zoological Codes of Nomenclature that ensure one taxon is assigned a single name for the purposes of unambiguous communication of names. How biogeographers discover natural areas is another topic entirely and should not be confused with area nomenclature.

The biogeographic names proposed by de Candolle (1820), Prichard (1826), Schouw (1823), Wagner (1844, 1845, 1846a, 1846b) and Schmarda (1853) are not included in the synonyms, because they were published before Sclater’s (1858) regionalisation. We apply a criterion analogous to the nomen conservandum convention of taxonomical nomenclature to provide a greater stability (Morrone 2014). Changing well known area names from the Sclaterian–Wallacean system to the names used by these authors will only confuse the area nomenclature further. Given that areas such as the Nearctic and Palearctic are already widely used in the biogeographic literature, keeping them seems to be prudent and in keeping with a stable area nomenclature.

Area taxonomy

Nearctic region: Sclater (1858)

Nearctic region: Sclater (1858, p. 142); Kirby (1872, p. 437); Wallace (1876b, p. 114); Sharpe (1884, p. 102); Heilprin (1887, p. 62); Sclater (1894, p. 98); Sclater and Sclater (1899, p. 153); Bartholomew et al. (1911, p. 10); Darlington (1957, p. 442); Rapoport (1968, p. 94); Morrone (2002, p. 150, 2006, p. 469); Procheş and Ramdhani (2012, p. 263); Kreft and Jetz (2013, p. 343-c); Rueda et al. (2013, p. 2217); Ribeiro et al. (2014, p. 249); Morrone (2015a, p. 84); Escalante (2017, p. 357); Hermogenes de Mendonça and Ebach (2020, p. 721); Escalante et al. (2021, p. 354).

North American region: Sclater (1858, p. 142).

American region: Murray (1866, p. 311) (in part).

Nearctic province: Huxley (1868, p. 315).

Neoseptentrional subregion: Blyth (1871, p. 427).

North American region: Kirby (1872, p. 437); Diels (1908, p. 148); Cox (2001, p. 519).

North Temperate realm: (in part) Allen (1892, p. 207).

Anglogean kingdom: Gill (1885, p. 17).

Arctamerican kingdom: Gill (1885, p. 17).

Nearctica area: Clarke (1892, p. 380).

Boreal region: Merriam (1892, p. 22).

Nearctic subregion: Newton (1893, p. 333); Schmidt (1954, p. 328); Poynton (1959, p. 26); Thorne (1963, p. 333); Smith (1983, p. 462); Stoddart (1992, p. 278); Morrone (1996, p. 104).

Sonoran region: Lydekker (1896, p. 363).

Sonoran kingdom: Schilder (1956, p. 76).

Nearctic kingdom: Udvardy (1975, p. 14); Morain (1984, p. 151); Udvardy (1987, p. 187); Kreft and Jetz (2010, p. 2044); Holt et al. (2013a, p. 75).

Madrean (Sonoran) subkingdom: Takhtajan (1986, p. 246).

North American–Atlantic region: Carta et al. (2022, table 2).

Diagnosis

Canada, mainland USA, central and northern Mexico and Greenland.

Remarks

So as to accommodate both the Nearctic and Holarctic in a single classification, without revising or synonymising these areas, we place the Nearctic and Palearctic as regions within the Holarctic kingdom.

Subregions

The Nearctic region comprises the Arctic, Western and Alleghany subregions (Escalante et al. 2021; Fig. 15).

Fig. 15.

The subregions and transition zone of the Nearctic region (after Escalante et al. 2021).

Palearctic region: Sclater (1858)

Palearctic region: Sclater (1858, p. 137); Kirby (1872, p. 432); Wallace (1876a, p. 180); Sharpe (1884, p. 104); Sclater (1894, p. 99); Sclater and Sclater (1899, p. 177); Bartholomew et al. (1911, p. 5); Schilder (1956, p. 76); Darlington (1957, p. 438); Poynton (2000, p. 39); Morrone (2002, p. 150); Procheş and Ramdhani (2012, p. 263); Kreft and Jetz (2013, p. 343-c); Rueda et al. (2013, p. 2217); Ribeiro et al. (2014, p. 249); Escalante (2017, p. 358); Morrone (2015a, p. 85); Escalante (2017, p. 358); Hermogenes de Mendonça and Ebach (2020, p. 721).

Europeo–Asiatic region: Murray (1866, p. 304).

Paleomeridional subregion: Blyth (1871, p. 427).

Paleoseptentrional subregion: Blyth (1871, p. 427).

North Temperate realm: (in part) Allen (1892, p. 207).

Eurasiatic kingdom: Gill (1885, p. 19).

Eurygean kingdom: Gill (1885, p. 19).

Eurasiatic region: Heilprin (1887, p. 58); Carta et al. (2022, table 2).

Palearctica area: Clarke (1892, p. 377).

Palearctic subregion: Newton (1893, p. 333); Schmidt (1954, p. 328); Poynton (1959, p. 26); Thorne (1963, p. 333); Smith (1983, p. 462); Morrone (1996, p. 104).

Eurasiatic region: Diels (1908, p. 145).

Palearctic kingdom: Udvardy (1975, p. 22); Morain (1984, p. 201); Udvardy (1987, p. 187); Kreft and Jetz (2010, p. 2044); Holt et al. (2013a, p. 75).

Tethyan (Ancient Mediterranean) subkingdom: Takhtajan (1986, p. 245).

Eurasian region: Cox (2001, p. 519).

Tethyan region: Lücking (2003, p. 43).

Diagnosis

Eurasia, northern China, Japan and Africa north of the Sahara.

Remarks

The Palearctic is included as a region within the Holarctic kingdom so as to accommodate to conflicting classifications (see discussion above).

Subregions

The Palearctic region has been classically divided into three subregions, namely European, Mediterranean and Siberian (Fig. 16). Further studies are still needed to corroborate them.

Fig. 16.

The subregions and transition (t.) zones of the Palearctic region (after Wallace 1876a).

Ethiopian region: Sclater (1858)

Ethiopian region: Sclater (1858, p. 138); Blyth (1871, p. 428); Kirby (1872, p. 434); Wallace (1876a, p. 251); Sharpe (1884, p. 105); Newton (1893, p. 345); Sclater (1894, p. 98); Lydekker (1896, p. 227); Sclater and Sclater (1899, p. 84); Bartholomew et al. (1911, p. 6); Newbigin (1913, p. 215); de Mello-Leitão (1937, p. 183); Darlington (1957, p. 428); de Lattin (1967, p. 280); Cabrera and Willink (1973, p. 27); Smith (1983, p. 462); Morrone (1996, p. 104); Kreft and Jetz (2013, p. 343-c); Rueda et al. (2013, p. 2217); Ribeiro et al. (2014, p. 249); Morrone (2015a, p. 85); Escalante (2017, p. 359); Hermogenes de Mendonça and Ebach (2020, p. 721).

Western Palæotropical region: Sclater (1858, p. 138).

Africano-Indian region: Murray (1866, p. 308).

Ethiopian province: Huxley (1868, p. 315).

Western Paleotropical region: Kirby (1872, p. 434) (in part).

Afrogean kingdom: Gill (1885, p. 20).

Ethiopian kingdom: Heilprin (1887, p. 82).

Indo-African realm: (in part) Allen (1892, p. 207).

Ethiopia area: Clarke (1892, p. 379).

Indo-African region: Diels (1908, p. 130).

Ethiopian subregion: Schmidt (1954, p. 328); Poynton (1959, p. 26); Smith (1983, p. 462).

African region: Schilder (1956, p. 76); Cox (2001, p. 519); Carta et al. (2022, table 2).

African subkingdom: Good (1963, p. 31); Takhtajan (1986, p. 247).

Africotropical kingdom: Udvardy (1975, p. 25); Morain (1984, p. 219); Fleming (1987, p. 199).

Afrotropical kingdom: Udvardy (1987, p. 187); Holt et al. (2013a, p. 75, 2013b, p. 343-d).

Afrotropical subregion: Morrone (1996, p. 104).

Afrotropical region: Poynton (2000, p. 39); Morrone (2002, p. 150); Procheş and Ramdhani (2012, p. 263).

African kingdom: Cox (2001, p. 519); Kreft and Jetz (2010, p. 2044).

African Paleotropics region: Lücking (2003, p. 43).

Southern African region: (in part) Carta et al. (2022, table 2).

Diagnosis

Central and southern Africa, the northern part of the Arabian peninsula, Madagascar and the West Indian Ocean islands.

Remarks

The Cape region of previous regionalisations is demoted to a subregion of the Ethiopian region following Carta et al. (2022) and Santos and Ribeiro (2022). Further studies using phylogenetic data within a comparative biogeographic analysis are needed to confirm this classification.

Subregions

The Ethiopian region comprises the following four subregions: East African, West African, Cape and Malagasy (Fig. 17).

Fig. 17.

The subregions and transition zone of the Ethiopian region (after Wallace 1876a).

Oriental region: Wallace (1876a)

Indian region: Sclater (1858, p. 140); Kirby (1872, p. 435); Sharpe (1884, p. 107); Newton (1893, p. 355).

Australasian region: Blyth (1871, p. 428).

Middle Paleotropical region: Kirby (1872, p. 435).

Oriental region: Wallace (1876a, p. 314); Heilprin (1887, p. 91); Sclater (1894, p. 98); Lydekker (1896, p. 264); Sclater and Sclater (1899, p. 123); Bartholomew et al. (1911, p. 7); Newbigin (1913, p. 217); de Mello-Leitão (1937, p. 196); Schilder (1956, p. 76); Darlington (1957, p. 433); Kuschel (1963, p. 447); Thorne (1963, p. 332); de Lattin (1967, p. 282); Cabrera and Willink (1973, p. 27); Stoddart (1992, p. 278); Morrone (2002, p. 150); Kreft and Jetz (2013, p. 343-c); Rueda et al. (2013, p. 2217); Ribeiro et al. (2014, p. 249); Morrone (2015a, p. 85); Escalante (2017, p. 359); Hermogenes de Mendonça and Ebach (2020, p. 721).

Indogean kingdom: Gill (1885, p. 19).

Oriental kingdom: Heilprin (1887, p. 90); Morain (1984, p. 239); Kreft and Jetz (2010, p. 2044); Holt et al. (2013a, p. 75).

Indo-African realm: (in part) Allen (1892, p. 207).

Indo-China area: Clarke (1892, p. 379).

Indo-African region: Diels (1908, p. 130).

Oriental subregion: Schmidt (1954, p. 328); Poynton (1959, p. 26); Smith (1983, p. 462); Morrone (1996, p. 104).

Palearctic region: (in part) Schilder (1956, p. 76).

Indo-Malaysian subkingdom: Good (1963, p. 31).

Malaysian region: Good (1963, p. 31).

Indomalayan kingdom: Udvardy (1975, p. 30) (in part).

Indo-Malesian subkingdom: Takhtajan (1986, p. 249).

Indomalayan kingdom: Udvardy (1987, p. 187).

Eastern Paleotropics region: Lücking (2003, p. 43).

Indo-Malaysian region: Procheş and Ramdhani (2012, p. 263).

Diagnosis

All areas south of the Tibetan Plateau and the Yellow River and west of Weber’s Line.

Remarks

A comparative biogeographic analysis by King and Ebach (2017) has shown that Palaeogene genera from Australia, southern New Guinea and eastern Sulawesi share a greater relationship to another than they do to Neogene genera (ages based on molecular dating). The results support Wallace’s Line as the border between the Oriental and Australian region, rather than Weber’s or Lydekker’s lines.

Subregions

The Oriental region comprises two subregions, Indian and Indo-Chinese (Fig. 18).

Fig. 18.

The subregions and transition zones of the Oriental region (after Wallace 1876a).

Neotropical region: Sclater (1858)

Neotropical region: Sclater (1858, p. 143); Kirby (1872, p. 437); Wallace (1876b, p. 3); Sharpe (1884, p. 102); Newton (1893, p. 321); Sclater (1894, p. 98); Lydekker (1896, p. 64); Sclater and Sclater (1899, p. 52); Bartholomew et al. (1911, p. 9); Newbigin (1913, p. 221); de Mello-Leitão (1937, p. 221); Schmidt (1954, p. 328); Schilder (1956, p. 76); Darlington (1957, p. 446); Poynton (1959, p. 26); Thorne (1963, p. 333); de Lattin (1967, p. 271); Rapoport 1968, p. 61); Cabrera and Willink (1973, p. 26); Stoddart (1992, p. 278); Morrone (2002, p. 150); Morrone (2006, p. 477); Procheş and Ramdhani (2012, p. 263); Rueda et al. (2013, p. 2217); Morrone (2014, p. 26); Ribeiro et al. (2014, p. 249); Morrone (2015a, p. 85); Escalante (2017, p. 358); Morrone (2017, p. 41); Hermogenes de Mendonça and Ebach (2020, p. 721).

American region: Murray (1866, p. 311) (in part).

Austro-Columbia province: Huxley (1868, p. 315).

Columbian region: Blyth (1871, p. 428).

South American region: Kirby (1872, p. 437); Cox (2001, p. 519).

Tropical America region: Engler (1882, p. 345).

Neotropica area: Clarke (1892, p. 381).

Tropical region: Merriam (1892, p. 33).

Neotropical subregion: Smith (1983, p. 462); Morrone (1996, p. 104).

Neotropics region: Lücking (2003, p. 43).

Diagnosis

The same as the subkingdom.

Subregions

The Neotropical region comprises three subregions, namely Antillean, Brazilian and Chacoan (Morrone 2014, 2017; Fig. 19).

Fig. 19.

The subregions and transition zones of the Neotropical region (after Morrone 2017).

Andean region: Engler (1882)

American region: Murray (1866, p. 311) (in part).

Andisian subregion: Blyth (1871, p. 427).

Peruvian subregion: Blyth (1871, p. 428); Thorne (1963, p. 333).

Chilean subregion: Wallace (1876b, p. 36) (in part); Bartholomew et al. (1911, p. 9); Thorne (1963, p. 333); Stoddart (1992, p. 278).

Andean region: Engler (1882, p. 346); Good (1963, p. 32); Morain (1984, p. 178); Takhtajan (1986, p. 251); Morrone (2002, p. 150, 2006, p. 483); Procheş and Ramdhani (2012, p. 263); Morrone (2015a, p. 86); Escalante (2017, p. 358); Morrone (2018, p. 43); Hermogenes de Mendonça and Ebach (2020, p. 721).

Anfigean kingdom: Gill (1885, p. 22).

South American Temperate kingdom: Allen (1892, p. 207) (in part).

Argentina subarea: Clarke (1892, p. 381) (in part).

Patagonian subregion: Sclater and Sclater (1899, p. 77); Sharpe (1884, p. 103); Newton (1893, p. 324); Poynton (1959, p. 26); Kuschel (1963, p. 447).

Andean dominion: Hauman (1931, p. 62).

Temperate South America dominion: Hauman (1931, p. 62).

Andean–Patagonian subregion: de Mello-Leitão (1937, p. 232); Rapoport (1968, p. 75).

Andean province: Schilder (1956, p. 76).

Patagonian region: Good (1963, p. 32); Takhtajan (1986, p. 253).

Andean–Patagonian dominion: Cabrera (1971, p. 29).

Austral subregion: Ringuelet (1975, p. 107).

Andean subkingdom: Rivas-Martínez and Tovar (1983, p. 516).

Argentine subregion: Smith (1983, p. 462).

Austroamerican subkingdom: Rivas-Martínez and Navarro (1994, map).

Neotemperate region: Amorim and Pires (1996, p. 187).

Andean subregion: Morrone (1996, p. 105).

Patagonian–Andean region: Daniels and Veblen (2000, p. 225).

Andean–Argentinian region: Carta et al. (2022, table 2).

Neozealandic–Patagonian region: (in part) Carta et al. (2022, table 2).

Diagnosis

Southern South America below 30° south latitude.

Remarks

Roig-Juñent et al. (2018) considered that the Patagonian biogeographic province should be considered as belonging to the South American transition zone, but we keep it in the Andean region.

Subregions

The Andean regions comprises three subregions, namely Subantarctic, Central Chilean and Patagonian (Morrone 2015b, 2018; Fig. 20).

Fig. 20.

The subregions and transition zone of the Andean region (after Morrone 2018).

Australian region: Sclater (1858)

Australian region: Sclater (1858, p. 141); Murray (1866, p. 310); Grisebach (1872, p. 203); Kirby (1872, p. 436); Wallace (1876a, p. 387); Engler (1882, p. 347); Sharpe (1884, p. 108); Heilprin (1887, p. 97); Newton (1893, p. 317); Sclater (1894, p. 97); Lydekker (1896, p. 30); Sclater and Sclater (1899, p. 18); Bartholomew et al. (1911, p. 8); Newbigin (1913, p. 223); de Mello-Leitão (1937, p. 209); Schmidt (1954, p. 328); Darlington (1957, p. 449); Poynton (1959, p. 26); Thorne (1963, p. 333); Cabrera and Willink (1973, p. 26); Stoddart (1992, p. 278); Cox (2001, p. 519); Procheş and Ramdhani (2012, p. 263); Rueda et al. (2013, p. 2217); Ribeiro et al. (2014, p. 249); Ebach et al. (2015, p. 266,) Morrone (2015a, p. 86); Escalante (2017, p. 359); Hermogenes de Mendonça and Ebach (2020, p. 721).

Western Paleotropical region: Sclater (1858, p. 141); Kirby (1872, p. 436) (in part).

Australian province: Huxley (1868, p. 315).

Australian subregion: Blyth (1871, p. 428); Schmidt (1954, p. 328); Kuschel (1963, p. 447); Thorne (1963, p. 333); Smith (1983, p. 462); Stoddart (1992, p. 278).

Austrogean kingdom: Gill (1885, p. 22).

Australian kingdom: Heilprin (1887, p. 97); Allen (1892, p. 207); Diels (1908, p. 156); Good (1963, p. 32); Udvardy (1975, p. 34); Morain (1984, p. 265); Müller (1986, p. 20); Takhtajan (1986, p. 252); Udvardy (1987, p. 187); Cox (2001, p. 519); Kreft and Jetz (2010, p. 2044); Holt et al. (2013a, p. 75); Kreft and Jetz (2013, p. 343-c); Ebach et al. (2015, p. 266).

Oceania area: Clarke (1892, p. 380).

Austral Oceanic subregion: Schilder (1956, p. 76).

Notogaeic kingdom: Lydekker (1896, p. 28).

Notogaean kingdom: Schmidt (1954, p. 328).

Island region: Smith (1983, p. 462).

Australasian kingdom: Fleming (1987, p. 199).

Australian subkingdom: Fleming (1987, p. 199); Carta et al. (2022, table 1).

New Guinean region: Procheş and Ramdhani (2012, p. 263).

Eremaean region: Carta et al. (2022, table 2).

Northern Australian region: Carta et al. (2022, table 2).

Diagnosis

Australian continent, New Guinea and western islands, eastern Sulawesi, southern Philippines, New Caledonia, and New Zealand.

Remarks

Wallace’s original classification is used herein, which includes the southern Phillipines.

Subregions

The Australian region comprises three subregions, namely Australian, Polynesian and New Zealand (Fig. 21).

Fig. 21.

The subregions and transition zone of the Australian region.

Transition zones

Areas that are defined through the overlap of two different kingdoms are called transition zones (sensu lato Morrone 2015a; sensu stricto Hermogenes de Mendonça and Ebach (2020; Table 5). Transition zones, by their composite nature, have no place in a hierarchal classification; rather they form a separate non-hierarchal classification detailed below.

Table 5.

The regions, divided into kingdoms, which overlap within transition zones (TZ).

Data availability

Data sharing is not applicable as no new data were generated or analysed during this study.

Conflicts of interest

Malte Ebach is an Associate Editor of Australian Systematic Botany but did not at any stage have editor-level access to this manuscript while in peer review, as is the standard practice when handling manuscripts submitted by an editor to this journal. Australian Systematic Botany encourages its editors to publish in the journal and they are kept totally separate from the decision-making processes for their manuscripts. The authors have no further conflicts of interest to declare.

Declaration of funding

This research did not receive any specific funding.