Proceratium Species Groups

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The following is based on Baroni Urbani, C., de Andrade, M.L. (2003), with additions from Hita Garcia et al (2014) and Staab et al (2018).

Arnoldi Clade

These species inhabit the African continent, except for P. galilaeum known only from Israel. The species belonging to this clade share a pair of transparent maculae on the vertexal angles and the presence of an often salient, transparent bulla on the posterior border of the postpetiole.

Hita Garcia et al (2014) - Diagnosis. The following diagnosis is based on Baroni Urbani and de Andrade (2003): clypeus reduced, only slightly protruding anteriorly, not surrounding the antennal sockets and not medially impressed; frontal carinae widely separated, not approaching each other closely and strongly diverging posteriorly; pair of transparent maculae on vertexal angles present in all but one species; calcar of strigil without basal spine; bulla usually located medially at the posterior end of the third abdominal segment; lower mesopleura posteriorly inflated.

Notes. Baroni Urbani and de Andrade (2003) gave the presence of transparent maculae on the vertexal angles and a bulla located medially at the posterior end of the third abdominal segment as characteristic of the clade. Nevertheless, the maculae are not present in all five species. Actually, in the new species P. carri there is not a trace of maculae on the vertexal angles, whereas all other clade members (including the eighth species of the clade P. galilaeum de Andrade from Israel) possess very conspicuous maculae. The holotype of P. arnoldi seemed to lack the maculae at first sight, but closer examination under higher magnifications and different light settings revealed them later. The other clade-specific character, the bulla on the third abdominal segment, is indeed present in all species of the P. arnoldi clade, even though it is much less developed in P. arnoldi and P. carri than in the remainder of the clade. Nevertheless, even though these characters are not always fully developed, the seven Afrotropical species of the P. arnoldi clade can be easily distinguished from the single Afrotropical species of the P. stictum clade and the two species of the P. toschii clade with the diagnosis given above.

Identification Key

Key to Afrotropical species of the Proceratium arnoldi clade

Itoi Clade

The workers of this clade share the following character: first gastral sternite (fourth abdominal) protruding over the third abdominal sternite (postpetiole).

Staab et al. (2018) - Workers of this clade can be separated from all other Proceratium species by the combination of abdominal sternum IV protruding over the posterior end of abdominal sternum III, petiolar node nodiform, and body sculpture densely granulate to punctate (definition follows Baroni Urbani and de Andrade 2003).

This clade includes seven species and is restricted to east and southeast Asia. All species except Proceratium malesianum and Proceratium williamsi occur in China. The species are morphologically similar, particularly in relative body proportions and indices, but can be safely separated with Key to Chinese Proceratium.

The subpetiolar process of Proceratium bruelheidei is well developed and roughly trapezoid in all available specimens, its size, exact shape, and ventral outline vary. In the holotype (CASENT0790023) and several paratypes (CASENT0790025, CASENT0790026, CASENT0790029) the subpetiolar process has a distinct notch, so that it almost looks like an upside-down volcano. This notch is absent in other specimens (CASENT0790027, CASENT0790028, CASENT0790030), where the ventral outline of the process is straight. In one specimen (CASENT0790024) the ventral outline is also straight but with a row of minute denticles. It thus appears that this character, which is often used to delimitate Proceratium species (e.g. Baroni Urbani and de Andrade 2003, Hita Garcia et al. 2014), may be less suitable for species in the Proceratium itoi clade, as also indicated by the variation in the subpetiolar process within the type series of Proceratium zhaoi.

Identification Key

Key to Chinese Proceratium

Micrommatum Clade

The species of the micrommatum clade are distributed from south Texas to south Brazil. The members of the clade share the following combination of synapomorphies: traces of a transversal propodeal sulcus in the worker, worker and gyne mid basitarsi with at least a hair long 1/2 or more of the basitarsus (this character seems to have been secundarily lost in 4 species, cubanum, dominicanum, longiscapus and taino), worker and gyne with first gastral tergite partially or entirely granulate, (this character is shared by the basal species of the micrommatum clade only), worker, gyne and male (when known) with palp formula 3,2.

P. transitionis appears in our analysis as the basalmost species of the micrommatum clade and lattkei results as the next in-group species of transitionis. Transitionis and lattkei are the most peculiar species of the clade. In fact both resemble in some characters the species of the goliath group by sharing with them the broad diverging frontal carinae and the dense and long pilosity. However, they share with all the remaining Proceratium species the mid legs with a spur, a character absent in all the other species of the micrommatum clade.

The other 13 species of the micrommatum clade are very similar to each other and often difficult to differentiate. These species can be easily separated from the two basal species, transitionis and lattkei, by the lack of spurs on the mid legs and by the narrow, raised frontal carinae.

Identification Key

Key to Proceratium micrommatum clade

Microsculptum Clade


Microsculptum shares with the members of the stictum clade and with the basalmost species of the micrommatum clade, transitionis, the anterior clypeal border broad and protruding anteriorly.

Microsculptum shares with terroni and toschii (the sole two species of the toschii clade) the frontal carinae very close to each other and fused posteriorly. It shares with three members of the pergandei clade (cornpitale, creek and confinium) the first funicular joint 1/2 longer than broad. With the six species of the pergandei clade and with two species of the itoi clade it shares the propodeum with lateral lamellae. Microsculptum, in addition, shares with the members of the itoi clade the gastral sternite II protruding over the postpetiolar sternite.

Microsculptum, in addition, results characterised by 4 autapomorphies: frontal carinae close each other and posteriorly attached; first funicular joint 1/2 longer than broad; presence of propodeal lamellae and second gastral sternite protruding medially. All these peculiarities largely justify inclusion of this species in a clade of its own.

Pergandei Clade

Five species (californicum, chickasaw, creek, compitale and pergandei) are confined to the southern Nearctic Region and six to the southern Palaearctic.

The members of this clade share the following synapomorphy: worker, gyne and male, spur of fore tibiae with a basal spine. This character is synapomorphic for the 11 species of the pergandei clade in spite of its homoplastic occurrence in the species of the stictum clade. There are another two characteristic traits shared by the species of the pergandei clade: worker and gyne head without genal carinae, and funicular joints 2-10 about as broad as long. The synapomorphic status of both these characters, however, results as equivocal from our cladistic analysis.

Silaceum Clade

The main synapomorphies of this clade are, for the worker and gyne: mandibular base with light macula, mid basitarsi with at least one hair 1/2 of the basitarsal length and arolia small or absent. Three other characters uniquely shared by the members of the silaceum clade are: worker and gyne: palp formula 2,2 and male palp formula 5,2 and clypeus anteriorly straight to weakly concave. These do not emerge as synapomorphic because of their equivocal ancestral state. Two species, relictum and oceanicum, both from the Fiji Islands, can be easily separated from the remaining 27 included in this clade by the petiole squamiform and with thin apex. They rnay constitute a small and homogeneous group within the clade: all the remaining species have a rectangular petiole and are much more difficult to characterize.

One species, longigaster from Vietnam, is currently placed here but it is insufficiently known. We were unable to examine specimens for this study.

Staab et al. (2018) - Workers of this clade can be distinguished by a moderately squamiform petiolar node that narrows only little from base to apex (extremely squamiform in the Fiji archipelago, Hita Garcia et al. 2015) and by an almost straight to weakly concave anterior clypeal margin (definition follows Baroni Urbani and de Andrade 2003).

The Proceratium silaceum clade sensu Baroni Urbani and de Andrade (2003) is, with more than 30 species, the most speciose and widespread clade within the genus. Numerous species occur in, respectively, Borneo and Australia. Species of this clade have been reported from all continents and several have reached oceanic islands. From China and east Asia only two species, Proceratium japonicum and Proceratium longigaster, are known.

Stictum Clade

This clade corresponds to the former stictum group of Brown (1958a, 1974) originally comprising four species only: stictum, goliath, aviurn and boltoni. Another four species were added by subsequent publications: diplopyx, deelemani, denticulatum, and tio. In this paper we describe another four species belonging to the same clade: avioide, gibberum, foveolatum and cavinodus.

The members of the stictum clade share the following worker, gyne and male synapomorphy: the presence of a basal spine on the protibial spur. This character results synapomorphic for the stictum clade in our analysis but it is also present in all the members of the phylogenetically distant pergandei clade. Lattke (1990) already described this character under the name of 'seta of the protibial spur' for the fossil species denticulatum.

Five species within the stictum clade appear in a distinct group named here as goliath group: deelemani, foveolatum, goliath, stictum and tio. These species share the following synapomorphy: worker and gyne with gular area deeply concave (char. 24). They also share large, deep, irregular roveae and granulation on the head, mesosoma, petiole and postpetiole and dense, long hairs. We did not use these characters for the cladistic analysis because the sculpture is less impressed in stictum, the basal species of the goliath group and similar sculptures can be found also among members of other clades like the micrommatum and arnoldi clades. In an analogous way, a pubescence similar to that of the goliath group can be encountered in members of the micrommatum and silaceum clades.

Five of the remaining 7 species of the stictum clade constitute a group of species named here as avium group. This group comprises the following species: avium, avioide, gibberum, denticulatum and diplopyx. These five species share synapomorphically the antennal joints 2-10 at least as broad as long. This trait is also shared by other species of a far clade.

Two species, boltoni and cavinodus appear in an unresolved position within the clade. P. boltoni and cavinodus in general morphology resemble the fossil members of the avium group: gibberum and denticulatum. This similarity is supported by the following characters: integument reticulate-foveolate and granulate, subpetiolar process spiniform, and with the fossil denticulatum only, frontal carinae low and subparallel and clypeal notch laterally denticulate.

The 12 species of the stictum clade appear to be irregularly distributed in the tropics of the world. Goliath and tio are known respectively from Mexico and Costa Rica, gibberum and denticulatum from Dominican amber, foveolatum from Malaysia, boltoni from Ghana, cavinodus and stictum from Australia, avium and avioides from Mauritius, diplopyx from Madagascar, and deelemani from Thailand and Malaysia.

Brown (1958a, 1974) considers the shape of the clypeus, of the mandibles and of the petiole of the species of this clade as 'primitive' within the genus Proceratium. This assumption is probably based on the fact that a nodiform petiole is likely to better represent the ponerine ancestral condition than the squamiform petiole "type Sysphincta". Unfortunately there is no morphological evidence for this since the two genera closer to Proceratium have a petiole either scale-like (Bradoponera) or scale-like to weakly nodiform (Discothyrea). We are unable to define two or more clear-cut mandibular morphologies to be used as discrete characters for phylogenetic purpose within Proceratium. According to the character evolution compatible with our phylogenetic reconstruction, however, the plesiomorphic clypeal morphology for Proceratium should be either convex and protruding (like in Discothyrea and Bradoponera), or straight (like in the basal silaceum clade). The members of the stictum clade, with their notched clypeus, appear to exhibit the derived and not the plesiomorphic clypeal morphology.

Staab et al. (2018) - Worker of this clade can be separated from all other Proceratium by the combination of calcar of strigil with a basal spine and clypeus distinctly and broadly notched (definition follows Baroni Urbani and de Andrade 2003).

This is an exclusively tropical clade with species occurring in Africa, Australia, Madagascar, the Mascarene Islands, Mesoamerica, and tropical southeast Asia. Eleven extant species are known, of which Proceratium deelemani, Proceratium foveolatum, Proceratium stictum, and the newly described Proceratium shohei are known from the oriental zoogeographic region. Proceratium shohei is the only species known from China.

Toschii Clade

African tropics.

Toschii and terroni share the blunt propodeal spines and the frontal carinae very close to each other and posteriorly fused. Another character shared by these two species is the first gastral sternite strongly protruding anteriorly. This character is not specifically considered in our cladistic analysis because it appears in an unpredictable way among the other species of the genus.