Caesalpinioideae sensu LPWG (2017) is the second largest subfamily of legumes with ca. 4680 species placed in 163 genera (Hughes et al. 2022a; LPWG 2022; Ringelberg et al. 2022). Within this subfamily, ca. 3500 species and 100 genera are placed in the former subfamily Mimosoideae (the mimosoid clade of LPWG 2017), which we here recognise as the reinstated, but newly circumscribed, tribe Mimoseae, a tribal name first published by Bronn in 1822 (see below). Caesalpinioideae date to the late Paleocene when the subfamily is known from fossil bipinnate leaves from Colombia (Wing et al. 2009; Herrera et al. 2019). These fossils indicate that Caesalpinioideae were an abundant element in the earliest Neotropical rain forests in the Paleocene and time-calibrated legume phylogenies suggest that Caesalpinioideae started to diversify around 58 million years ago (Lavin et al. 2005; Bruneau et al. 2008; Koenen et al. 2021). Caesalpinioideae have thus diversified throughout the Cenozoic and now comprise diverse, abundant, and sometimes dominant elements across all major lowland tropical biomes, including rain forests, savannas and seasonally dry forests (Figs 1, 2, 3).

Figure 1. 

A Caesalpinioideae genus richness across floristic realms (according to Liu et al. 2023). The numbers within the circles represent the total number of genera in each realm. The numbers on the lines represent the number of genera shared between two realms (> 10 genera) B Number of Casalpinioideae genera in the floristic subrealms (sensu Liu et al. 2023). The numbers associated with the two polygons indicate the number of genera restricted to the two major blocks of tropical and subtropical areas in the New World and the Old World (maps modified from Liu et al. 2023, CC BY 4.0).

Figure 2. 

Map showing the global distribution of Caesalpinioideae species richness. Numbers of Caesalpinioideae species per one degree latitude / longitude grid cell. Infraspecific taxa are not counted individually but are included at the species level. All maps in this special issue are based on quality-controlled occurrence data from digitised herbarium specimens and floristic surveys (see Suppl. material 1 for details on occurrence data and methods used to generate maps).

Figure 3. 

Map showing the global distribution of Caesalpinioideae genus richness. Numbers of Caesalpinioideae genera per one degree latitude / longitude grid cell.

Caesalpinioideae are almost entirely woody perennials, but they are extremely diverse in stature and habit – including lianas, trees of all sizes, up to rain forest canopy emergents (e.g., Cedrelinga Ducke, Dinizia Ducke), shrubs, functionally herbaceous geoxyles, and two herbaceous aquatic species (Neptunia Lour.). Similarly, the subfamily is highly diverse in floral and fruit morphology. One of the hallmarks of Caesalpinioideae, as in many other plant groups, is repeated morphological and ecological convergences whereby similar leaf, flower and fruit morphologies, and ecological adaptations, have apparently been reinvented multiple times across lineages and through time (Ringelberg et al. 2022, 2023).

Caesalpinioideae is the only legume subfamily that has bipinnate leaves, which are prevalent but not universal across the subfamily (see Glossary, Schemes 1–7). A minority of genera have species with pinnate leaves, and leaves modified into phyllodes occur in most species of the large, mainly Australian, genus Acacia Mill. and in a few species in other unrelated genera including Senna Mill. and Mimosa L. The leaves themselves, especially the bipinnate leaf, can be extremely large (e.g., Schizolobium Vogel leaves are > 1 m long) to highly reduced; aphyllous, or nearly aphyllous, species occur in some genera [e.g., Acacia, Senna, Chamaecrista (L.) Moench, Neltuma Raf., Prosopidastrum Burkart]. Across all legumes, seismonasty, i.e., leaf movements prompted by touch, is known only within subfamily Caesalpinioideae, in the genera Mimosa and Neptunia (tribe Mimoseae). Extrafloral nectaries (EFNs) are present in the majority of Caesalpinioideae (Scheme 2), are morphologically extremely diverse, and often conspicuous and abundant on the petiole or leaf rachides between pinnae or leaflet pairs, and in a few genera (e.g., Archidendron F. Muell., Macrosamanea Britton & Rose) on floral bracts (Marazzi et al. 2019). A subset of Caesalpinioideae genera are armed with prickles, spines or thorns (Scheme 1), but armature is highly variable, has clearly evolved multiple times across the subfamily, and can vary within clades and even within genera (Hughes et al. 2022a; Ringelberg et al. 2022). Most genera of the mimosoid clade (tribe Mimoseae here) are confirmed nodulators, whereas just nine of the 63 non-mimosoid genera in the subfamily are currently known to nodulate. These nine genera are phylogenetically intermingled with confirmed non-nodulating genera, suggesting multiple evolutionary transitions between non-nodulating and nodulating lineages (Faria et al. 2022). Analyses of gene duplications have shown that several whole genome duplications (WGDs) occurred during the early evolution of the family Leguminosae (Cannon et al. 2015; Stai et al. 2019; Koenen et al. 2021; Zhao et al. 2021), although the exact number and placement of these WGDs remain uncertain. Within Caesalpinioideae, polyploidisation has also occurred numerous times during the Neogene in several genera across the subfamily [e.g., Leucaena Benth., Dichrostachys (A. DC.) Wight & Arn., Neptunia, Vachellia Wight & Arn., Mimosa; Dahmer et al. 2011; Govindarajulu et al. 2011a; Simon et al. 2011].

Across the subfamily, inflorescences and flowers are morphologically highly variable. The inflorescences can be racemose, paniculate or in fascicles and the Mimoseae have characteristic capitate or spicate and frequently heteromorphic inflorescences, often with some sterile flowers, some of which develop showy staminodia (Schemes 3, 4). Although usually bisexual, flowers can also be unisexual, and in the Mimoseae inflorescences can include a mixture of both bisexual and unisexual flowers with or without sterile flowers. The flowers are generally pentamerous, but there are many variations [3–6 (8) sepals or petals], and in some species, sepals and/or petals are absent (Ceratonia L.). Flowers are generally radially symmetrical in several Caesalpinioideae tribes, including the Mimoseae, but in other clades the flowers are bilaterally symmetrical or asymmetrical. Although a majority of Caesalpinioideae flowers are bee pollinated, specialised bat, bird, butterfly and moth pollinated flowers are also common (Arroyo 1981). In addition to having species with pollen in the more typical tricolporate monads, Caesalpinioideae is the only subfamily of legumes with taxa where pollen is arranged in polyads (Scheme 6). In Mimoseae the pollen arrangement is extremely variable across and sometimes within genera, with pollen in monads, tetrads, bi-tetrads and polyads. Fruit morphology is particularly homoplasious, and in the Mimoseae has proved misleading for generic delimitation (Borges et al. 2022; Ringelberg et al. 2022; Souza et al. 2022b). This diversity of fruit morphology (Schemes 6, 7) reflects adaptations to different seed dispersal syndromes, including passive, elastic and explosive dehiscence, as well as seed dispersal by water, wind, large herbivores, ants, and birds.

The subfamily is most diverse in lowland tropical and subtropical regions, only rarely occurring above 2500 m elevation, but a minority of genera have species in warm temperate zones that are not prone to severe frosts across the Americas, Europe, Asia, and Australia. More than half of Caesalpinioideae genera naturally occur in the Americas (104 of 163 genera), of which 84 are endemic. Africa (including Madagascar) has the second highest number of Caesalpinioideae genera, with 59 genera, 29 of which are endemic, followed by Asia (40 genera, 7 endemic), and Australia and the Pacific (27 genera, 6 endemic; See details in Tables 1, 2).

The Neotropical floristic realm (sensu Liu et al. 2023) has 101 Caesalpinioideae genera with native species, of which 71 are endemic to this realm (Table 1). Liu et al. (2023) divided the Neotropical realm into the tropical Brazilian subrealm (81 genera, 25 endemic) and the Subtropical American subrealm (76 genera, 17 endemic). The Subtropical American subrealm includes the northern (69 genera, 13 endemic) and southern (35 genera, 3 endemic) extremes of the Neotropical region (Fig. 1). The genera Strombocarpa (Benth.) Engelm. & A. Gray and Prosopidastrum Burkart are restricted to this subrealm and have an amphitropical distribution, whereas the genera Erythrostemon Klotzsch and Desmanthus Willd. have a similar distribution, but with a few species reaching the Brazilian subrealm. The second largest floristic realm for Caesalpinioideae genera is the African one, with 59 genera, of which 30 are endemic, primarily in the Guineo-Congolian subrealm (41 genera, 14 endemic). Within the Indo-Malesian realm, there are 40 genera (11 endemic), almost evenly distributed between the Indian (29 genera, 4 endemic) and the Malaysian subrealms (32 genera, 5 endemic).

Nine genera have a pantropical distribution, occurring in all tropical floristic realms [Cassia L., Chamaecrista, Entada Adans., Guilandina L., Neptunia, Peltophorum (Vogel) Benth., Senegalia Raf., Senna, Vachellia; Table 2]. The genera Mimosa and Parkia R. Br. occur in all tropical floristic realms except for the Australian realm. Seven genera (Adenopodia C. Presl, Denisophytum R. Vig., Haematoxylum L., Hydrochorea Barneby & J.W. Grimes, Parkinsonia L., Pentaclethra Benth., Pomaria Cav.) represent transatlantic disjunctions as they are exclusively distributed in the Neotropical and African realms.

The genera in Caesalpinioideae are geographically arranged across two major continental blocks. The American block, including the entire Neotropical realm, the Chile-Patagonian realm, and the southern part of the Holarctic realm (North American subrealm), has 83 genera restricted to it, with eight of these genera distributed across the Neotropical and Chile-Patagonian realms, some slightly extending to the southern portion of the North American subrealm (Acaciella Britton & Rose, Calliandra Benth., Desmanthus, Erythrostemon, Hoffmannseggia Cav., Mimozyganthus Burkart, Neltuma, and Strombocarpa). The second major block includes the African, Indo-Malesian, and Australian realms, with 52 genera restricted to this block and with Adenanthera L., Dichrostachys, Erythrophleum Afzel. ex R. Br., and Mezoneuron Desf. occurring in all three of these realms. Acacia weakly extends into the Madagascan (La Réunion and Mauritius) and Tasmanian subrealms.

Species richness, determined from occurrence records, indicate south-central Mexico and Central America, central-eastern Brazil, and southwestern Australia to be the most diverse regions (Fig. 2), with multiple one-degree grid cells in these regions containing more than a hundred Caesalpinioideae species. However, patterns of generic richness (Fig. 3) show that the high species diversity in Australia is largely attributable to the hyper-diverse genus Acacia, with over a thousand species. Australia is therefore characterised by high species but low generic richness. Important hotspots of Caesalpinioideae diversity also occur in continental Africa and Madagascar. Asia is the least diverse tropical continent, although it contains multiple species-rich lineages such as Archidendron, especially in South East Asia. The spatially biased availability of digitised occurrence data (Meyer et al. 2016) leads to an underestimation of Caesalpinioideae richness across large parts of tropical Africa, India, continental South East Asia, and the Amazon, as is apparent in Figs 2, 3. Nevertheless, our analyses (Figs 2, 3) represent an accurate depiction of relative differences in Caesalpinioideae continental richness patterns (Table 1).

The wide geographical distribution of Caesalpinioideae is matched by an equally wide ecological amplitude across the full precipitation spectrum of the tropics, spanning a 100-fold gradient in mean annual precipitation from arid deserts to seasonally dry tropical forests and savannas, and tropical rainforests (Schrire et al. 2005a; Gagnon et al. 2019; Ringelberg et al. 2023). Although Caesalpinioideae species are important components of many wet regions of the world, it is notable that some of the major hotspots of species and especially generic diversity coincide with areas dominated by seasonally dry vegetation in southern Mexico, north-eastern Brazil, and northern and south-western Madagascar, these being key areas of the succulent biome sensu Schrire et al. (2005a) and Ringelberg et al. (2020), plus seasonally dry subtropical south-western Australia. The subfamily thus has no obvious overriding wet or dry affinity, but rather has switched between wet and dry tropical biomes multiple times and has diversified substantially within each (Ringelberg et al. 2023). This ecological adaptability is undoubtedly, at least in part, a function of the evolutionary lability of life history strategies, including adaptations to fire, which has allowed Caesalpinioideae species to become important, diverse, and abundant elements of all lowland tropical biomes. It is also clear that Caesalpinioideae have been able to disperse across oceans numerous times to reach all tropical continents and the majority of lower latitude islands and island archipelagos (Figs 1, 2, 3). In contrast to this wide adaptability across tropical precipitation regimes and vegetation types, Caesalpinioideae show high tropical niche conservatism and very limited adaptability to cold temperatures and frost with just a small subset of lineages and species extending into temperate vegetation (Ringelberg et al. 2023).

Stability is one of the most important qualities of any taxonomic classification. It is therefore crucial that the phylogenetic framework used for assigning names to clades is robust and unlikely to change with sampling of additional taxa or genomic regions in the future. Based on the number and identity of the taxa included, the size of the genomic dataset, and the phylogenomic methods used to infer the phylogeny and assess its robustness, the phylogenetic framework employed here is currently the best available for taxonomic classification of Caesalpinioideae. This is confirmed by its overall agreement with previous smaller-scale phylogenies (see details below) and other recent independent phylogenomic studies (Zhang et al. 2020; Zhao et al. 2021). Furthermore, throughout this compendium the phylogeny is presented in such a way to allow easy assessment of underlying genomic support for all nodes subtending named clades, and in general clades named here are subtended by well-supported nodes on long branches. Absolute stability can never be guaranteed, and sampling of additional taxa might well result in different topologies and generic re-delimitation in some parts of the tree, such as in the Senegalia grade (Terra et al. 2022) or the Archidendron clade (Brown et al. 2022; Demeulenaere et al. 2022). Nevertheless, we consider the phylogenomic framework robust, and an adequate basis for the new classification presented here.

The classification proposed here uses as its framework the most comprehensively sampled phylogenetic analysis of Caesalpinioideae to date (Figs 4, 5, Suppl. materials 2, 3). This new phylogeny is based on Koenen et al. (2020a) and Ringelberg et al. (2022, 2023). By developing a clade-specific bait set for targeted enrichment of 964 nuclear genes, Koenen et al. (2020a) generated a DNA sequence dataset an order of magnitude larger than those used previously, thereby providing the greatly enhanced phylogenetic resolution required for classifying tribe Mimoseae. Capitalising on these foundations using a slightly modified version of the gene set covering 997 nuclear genes, and importantly extending the taxon sampling to include 300 additional species covering not only Mimoseae but also most genera of non-mimosoid Caesalpinioideae, as well as conducting transcontinental sampling of genera that occur across different continents, Ringelberg et al. (2022, 2023) established a robust phylogenomic hypothesis for subfamily Caesalpinioideae as a whole. These studies revealed or confirmed the non-monophyly of 22 genera, and this was the basis for the re-circumscription of 15 of these genera presented in Advances in Legume Systematics 14, Part 1 (Hughes et al. 2022a).

Figure 4. 

Phylogeny of Caesalpinioideae showing the tribal classification presented here. The names and phylogenetic placements of all 63 non-Mimoseae Caesalpinioideae genera are shown and known generic non-monophyly is indicated with terminal names of non-monophyletic genus in bold. The most likely placements for four unsampled genera are indicated with dashed lines; see respective treatments for details. Tribe Mimoseae has been collapsed (see Fig. 5). Branch lengths are expressed in coalescent units, and terminal branch lengths have been assigned an arbitrary uniform length for visual clarity. Monophyletic genera are represented by single branches; see Suppl. material 2 for a phylogeny with all accessions. See Suppl. material 3 for gene tree support across the phylogeny. The phylogeny is a pruned version of the backbone phylogeny of Ringelberg et al. (2023), where full details of the data and phylogenomic analysis methods are presented.

Figure 5. 

Phylogeny of tribe Mimoseae showing the clade-based classification of the tribe with two named higher-level and 17 named lower-level clades. The names and phylogenetic placements of all 100 Mimoseae genera are shown, and known generic non-monophyly is indicated with terminal names of non-monophyletic genera in bold. The most likely placement of the unsampled genus Microlobius is indicated with a dashed line; see Stryphnodendron clade treatment (page 319) for details. Branch lengths are expressed in coalescent units, and terminal branch lengths have been assigned an arbitrary uniform length for visual clarity. Monophyletic genera are represented by single branches; see Suppl. material 2 for a phylogeny with all accessions. See Suppl. material 3 for gene tree support across the phylogeny. The phylogeny is a pruned version of the backbone phylogeny of Ringelberg et al. (2023) where full details of the data and phylogenomic analysis methods are presented.

The phylogenomic analysis presented here includes 420 Caesalpinioideae species representing all but five of the 163 genera. The five missing genera are: Vouacapoua Aubl., which has three species and is likely a member of tribe Cassieae (e.g., Bruneau et al. 2008; LPWG 2017; Kates et al. 2024); Pterogyne Tul., placed here in a phylogenetically isolated, monospecific tribe (e.g., Bruneau et al. 2001, 2008; Manzanilla and Bruneau 2012; Zhang et al. 2020; Zhao et al. 2021); Stenodrepanum Harms and Hultholia Gagnon & G.P. Lewis, both monospecific genera of tribe Caesalpinieae (Gagnon et al. 2016); and Microlobius C. Presl, a monospecific genus in the Stryphnodendron clade of tribe Mimoseae (Lima et al. 2022). Although only about 10% of species were sampled in the analyses underlying the phylogenies presented here, several lower-level phylogenetic analyses of specific clades have been published and provide additional support for the groupings presented (Ringelberg et al. 2022). Furthermore, taxon sampling was specifically designed to cover taxonomic diversity spanning the root nodes of subclades and genera (Koenen et al. 2020a; Ringelberg et al. 2022, 2023).

Scheme 1. 

Scheme 2. 

Scheme 3. 

Scheme 4. 

Scheme 5. 

Scheme 6. 

Scheme 7. 

A common feature of phylogenomic analyses employing large numbers of genes is the presence of conflict among gene trees, i.e., phylogenies based on individual genes (Salichos and Rokas 2013; Koenen et al. 2020a, 2020b, 2021; Zhang et al. 2020). Such gene tree conflict is widespread across many nodes in the Caesalpinioideae phylogeny presented here (Koenen et al. 2020a; Ringelberg et al. 2022, 2023). The main cause of this conflict appears to be lack of signal for many nodes in individual gene trees. In such cases, the relevant node in the species tree is only supported by a relatively small number of gene trees, but there is no strong support among the gene trees for any of the alternative, conflicting topologies. The presence of this type of gene tree conflict, indicative of lack of signal rather than true gene tree disagreement, does not preclude naming a clade subtended by such a node, as there is no strong reason to assume that including additional accessions or genomic regions would result in different relationships (Koenen et al. 2020a; Ringelberg et al. 2022). However, in a few places across the tree there is stronger support for alternative conflicting topologies (Koenen et al. 2020a; Ringelberg et al. 2022, 2023). In general, such instances of strong conflict are not found in nodes subtending clades named here, but rather in the relationships within clades [e.g., in parts of the Caesalpinieae (Fig. 34) and Archidendron clade (Fig. 225)] and between clades [e.g., the relationships between tribes Schizolobieae, Sclerolobieae, and Dimorphandreae (Suppl. material 3) or between the Adenanthera and Entada clades and Sympetalandra Stapf and Chidlowia Hoyle (Fig. 114)]. Similarly, strong gene tree conflict, including between the nuclear and chloroplast genomes, may affect generic delimitation in some parts of the tree, such as in Senegalia (Terra et al. 2022) and Dimorphandra Schott (Ringelberg et al. 2022). Where relevant for the new classification presented in this compendium, these instances of strong gene tree conflict are described below.

The reference phylogeny used here as the basis for the new classification was inferred using ASTRAL (Zhang et al. 2018), deploying the multi-species coalescent approach based on individual gene trees, which performs well on datasets with inter-genic conflict (Jiang et al. 2020). We always report the non-significant (i.e., > 0.05) outcomes of the ASTRAL polytomy test (Sayyari and Mirarab 2018), which tests for each node whether the polytomy null model can be rejected. Because conventional phylogenetic support metrics, such as bootstrap support, tend to be inflated in large phylogenomic datasets (Rokas and Carroll 2006), we report support for nodes in the species tree using measures of individual gene tree conflict and concordance, calculated using PhyParts (Smith et al. 2015) (Suppl. material 3). The impacts of phylogenomic methods and the presence of conflict among different gene and species trees on taxonomic decisions were further discussed in Ringelberg et al. (2022). Full details of the phylogenomic data and analyses were presented in Ringelberg et al. (2023).

Under the LPWG (2017) subfamilial classification, subfamily Caesalpinioideae was the most difficult and controversial to delimit because of the inclusion of the formerly recognised, widely accepted and morphologically distinctive subfamily Mimosoideae. Abandoning the well-known Mimosoideae, an important disadvantage of adopting the six-subfamily classification, was mitigated by continuing to recognise this lineage as a named clade, informally referred to simply as the mimosoid clade until now (LPWG 2017), but here formally reinstated as the re-circumscribed and expanded tribe Mimoseae within the new Linnean tribal classification proposed here.

Although Mimoseae have traditionally been diagnosed by a series of diagnostic features, notably valvate petal aestivation and flowers with a reduced perianth and showy androecium, mostly clustered in compact inflorescences, the morphological distinctions between the mimosoid clade and some genera of the subtending grade of caesalpinioid lineages are not always clear-cut. For example, Dinizia, once considered to be in Mimosoideae, is placed outside the mimosoid clade in molecular phylogenetic and phylogenomic analyses (Luckow et al. 2003; Bruneau et al. 2008; Ringelberg et al. 2022). Conversely, Chidlowia, which has always been considered a non-mimosoid caesalpinioid legume (Polhill and Vidal 1981; Lewis 2005b), is placed within the mimosoid clade in all molecular phylogenetic analyses (Manzanilla and Bruneau 2012; LPWG 2017; Koenen et al. 2020a; Ringelberg et al. 2022). However, the long branch subtending what could be considered equivalent to the old subfamily Mimosoideae (plus or minus these few genera) (Fig. 4), together with the strong phylogenetic support for the clade, provide ample justification for recognising it at the tribal level.

The new classification proposed here thus follows a traditional Linnean approach but is complemented by a clade-based classification of the large tribe Mimoseae. Rank-free naming of clades within subfamilies and tribes has been prevalent in the legume literature, with many examples of clade names that have become widely used and accepted, such as the dalbergioid clade (Lavin et al. 2001) and the inverted repeat [IR]-lacking clade (Wojciechowski et al. 2000) of Papilionoideae; the Umtiza clade (Herendeen et al. 2003b) and the ingoid clade (Koenen et al. 2020a) of Caesalpinioideae; and the Bauhinia and Phanera clades of Cercidoideae (Sinou et al. 2020). Naming clades provides useful additional information even after a fully developed and stable subfamily and tribal classification is established. As noted by Wojciechowski (2013), use of Linnean names does not preclude a system that also defines and names clades and their overall relationships outside of the Linnean framework. Instead, the two can be considered complementary for developing a stable, flexible and useful classification of legumes.

The new classification of subfamily Caesalpinioideae comprises eleven tribes, which are either new, reinstated or re-circumscribed at this rank: Caesalpinieae Rchb., Cassieae Bronn, Campsiandreae LPWG, Ceratonieae Rchb., Dimorphandreae Benth., Erythrophleeae LPWG, Gleditsieae Nakai, Mimoseae Bronn, Pterogyneae LPWG, Schizolobieae Nakai, and Sclerolobieae Benth. & Hook. f. (Fig. 4). Although many of these lineages have been recognised and named in the past, either as tribes or informal generic groups, their circumscriptions have varied widely and changed over the past decades, such that all the tribes described here differ in generic membership from those previously recognised (Table 3).

Caesalpinioideae as defined here includes elements from three previously recognised major groups: part of old sense tribe Caesalpinieae, part of old sense tribe Cassieae, and the nested subfamily Mimosoideae. This broad clade has been referred to as the Mimosoideae-Caesalpinieae-Cassieae or MCC clade (Doyle 2011, 2012), or the Gleditsia-Chamaecrista-Mimosoideae or GCM clade (Marazzi et al. 2012). In 2017, Caesalpinioideae was chosen over Mimosoideae as the preferred name for this large clade, even though the two names were published at the same date (LPWG 2017). By choosing the name Caesalpinioideae, this left open the option of recognising the morphologically distinct mimosoid clade at the tribal level, as proposed here.

In their treatment of tribe Caesalpinieae in Advances in Legume Systematics Part 1, Polhill and Vidal (1981) recognised eight informal generic groups, based primarily on differences in floral morphology. Six of these generic groups, namely the Gleditsia group, Sclerolobium group, Peltophorum group, Caesalpinia group, Pterogyne group, and Dimorphandra group, are here recognised at the tribal level, albeit with modified generic compositions because most of Polhill and Vidal’s named groups have been shown to be non-monophyletic in subsequent phylogenetic analyses using molecular data (e.g., Bruneau et al. 2001, 2008) (Table 3). The monospecific Acrocarpus group of Polhill and Vidal (1981) groups with members of tribe Ceratonieae, rather than being considered a distinct tribe. In addition, the Caesalpinieae sensu Polhill and Vidal (1981) included the genus Poeppigia C. Presl. (as a distinct monogeneric group), which has since been shown to be placed in subfamily Dialioideae (Bruneau et al. 2001; LPWG 2017). Tribe Caesalpinieae of Polhill and Vidal (1981) had been considered to be paraphyletic, at least implicitly, for some time (Polhill and Vidal 1981; Lewis 1998) and this has since been confirmed by phylogenetic analyses which found the tribe to be polyphyletic (Bruneau et al. 2001). The other major group that forms part of Caesalpinioideae is what was considered tribe Cassieae by Irwin and Barneby (1981). Within the tribe, they recognised five disparate subtribes, Labicheinae H.S. Irwin & Barneby, Dialiinae H.S. Irwin & Barneby, Duparquetiinae H.S. Irwin & Barneby, Cassiinae Wight & Arn., and Ceratoniinae H.S. Irwin & Barneby, of which only the latter two have been placed in the Caesalpinioideae (sensu LPWG 2017) in phylogenetic analyses (Table 3). Labicheinae and Dialiinae together (along with Poeppigia) comprise subfamily Dialioideae, and the monospecific Duparquetiinae was raised to subfamily rank (LPWG 2017). Thus the grade of non-mimosoid caesalpinioid lineages that subtend tribe Mimoseae in Caesalpinioideae are here recognised as distinct tribes.

Below we provide a brief morphological description, overview of previous classification, and history of the phylogenetic understanding of each of the tribes proposed here. Additional details are given in the taxonomic accounts for each of these groups.