Crematogaster (subgenus)

A nominal subgenus of Crematogaster, and just one of two subgeneric names that were retained by Blaimer (2012c) in her revision of the higher-level relationships within the genus.

Introduction
Blaimer (2012c) stated: The two-subgenera system as proposed follows a deep molecular divergence event between Orthocrema and Crematogaster sensu stricto, tracing back into the Mid-Eocene (ca.40–45 Mya) when these two clades last shared a common ancestor (Blaimer, in press). Recognizing these two groups from each other on a morphological basis is fairly easily achieved, although a diagnosis of the Crematogaster sensu stricto is more problematic given the high morphological variability. An obvious further improvement to the system presented here would have been the recognition of the global Crematogaster clade and the Australo-Asian Crematogaster clade as separate subgeneric entities, as they certainly show enough molecular divergence to justify a three-subgenera-approach. I refrained from such a formal distinction since it was not possible to assign species to these groups on a morphological basis. At present, I encourage the use of the terms “global clade” and “Australo-Asian clade” for these lineages. I primarily aimed to develop a practical, ‘user-friendly’ classification. Petiole and postpetiolar characters that are useful for the distinction of Crematogaster sensu stricto and Orthocrema become hypervariable within the two sensu stricto clades and are not informative at deeper phylogenetic levels. Similar character patterns, for example the presence/absence of a median longitudinal impression on the postpetiole appear to have evolved multiple times within the genus, but the selective pressures acting on morphological evolution in Crematogaster have yet to be revealed. More biological data will need to be collected to investigate these questions.

The proposed species-groups are intended as a guideline on how to structure the large Crematogaster sensu stricto clade more finely, given the phylogenetic framework. I did not attempt to assign every species sampled within the phylogeny (or otherwise known to me) to a species-group. Many more natural groups will only become apparent when the phylogeny of the genus is extended and should thus be established sequentially as data become available. Finally, I conclude that the main advantage of recognizing monophyletic species-groups as suggested here is, that these present manageable subunits for taxonomic revisions. In addition, these species-groups will pose excellent subjects for (needed) comparative ecological and behavioural studies within Crematogaster.

subgenus Crematogaster global clade species groups
Comprises former members of subgenera Crematogaster sensu stricto (in part), Decacrema (part), Oxygyne (incl. Nematocrema), Mesocrema (in part), Colobocrema, Atopogyne and Sphaerocrema.


 * 1. Petiole shape varying from moderately (Fig. 14; figures at end of page), broadly (Fig. 15) or sharply flared (Fig. 16), oval (Fig. 18) or suboval (Fig. 19), elongate oval (Fig. 20) or hexagonal (Fig. 22).


 * 2. Postpetiole usually more or less bilobed (Figs 14b–19b, 22b), with a distinct longitudinal impression (e.g. Figs 14b–16b, 23); exception is the African C. kneri-group (see below), here postpetiole globular with at most a weak posterior impression (Figs 24–25).

Crematogaster ranavalonae group
Blaimer (2012c)

Crematogaster ranavalonae group - species list and diagnosis, plus additional details of the Asian species of the group

Key to Asian Crematogaster ranavalonae group species

Crematogaster castanea group
Blaimer (2012c)

1. Petiole usually broadly or moderately flared and distinctly wider than long, rarely reduced to a suboval form.

2. Postpetiole distinctly and broadly bilobed, usually with deep and broad median impression.

3. Head usually broad, often wider than long, with straight or medially depressed posterior margin and subangular corners.

This group includes members of the subgenus Crematogaster from Africa and Madagascar.

Key to Afrotropical Crematogaster castanea group


 * Crematogaster castanea
 * Crematogaster degeeri
 * Crematogaster dentata
 * Crematogaster excisa
 * Crematogaster flaviventris
 * Crematogaster gerstaeckeri
 * Crematogaster latuka
 * Crematogaster lobata
 * Crematogaster rufigena
 * Crematogaster sewellii

Blaimer (2012c) noted in her study there was a Malagasy clade, the C. degeeri-sewellii-group, of the C. castanea group, being revised. This follows below, and was presented as the C. degeeri assemblage. The evaluation of these ants called into question the validity and utility of the C. castanea group. This has not been addressed, and there are currently numerous species that are shared between the species group and the species assemblage.

Crematogaster degeeri assemblage
Blaimer and Fisher (2013) A group of Madagascar species.

No morphological characters that unite these ants have been discovered to date. This group was referred to in Blaimer (2012b) as the “Crematogaster degeeri-sewellii group”; after subsequent broadening by Blaimer (2012d) to include a few African species, it was hence dubbed the “C. castanea-group”. This grouping likely does not form a clade, but rather represents a group of loosely related species that may have closer affinities with African species (but see phylogeny in Blaimer 2012b). We choose here to revert to a description of the Malagasy species in this group only, since our taxonomic insight into the related African species is not yet sufficient. Most species in the C. degeeri-assemblage occur in Madagascar only, but three species are also found in the wider Malagasy region, including the Indian Ocean Islands of Comoros, Mayotte and Mauritius. The group is not present in the Seychelles.

The natural history and ecology of species within this group do not follow a common theme but are highly diverse. The C. degeeri-assemblage includes arboreal species nesting in dead twigs or branches, as well as ground-dwelling species found in nests under stones or in the soil. Ground-nesting is rather atypical for Crematogaster ants, which often dominate the canopy. All major macrohabitats are occupied by one or the other representative of the C. degeeri-assemblage in Madagascar: dry and spiny forests, littoral forest, rainforest, montane forest, savannah and grasslands, as well as coastal and mangrove habitat. A few species further appear to adapt quite well to urban or disturbed areas.

Key to Crematogaster degeeri species-assemblage.


 * Crematogaster alafara
 * Crematogaster bara
 * Crematogaster degeeri
 * Crematogaster dentata
 * Crematogaster lobata
 * Crematogaster mafybe
 * Crematogaster maina
 * Crematogaster malahelo
 * Crematogaster masokely
 * Crematogaster ramamy
 * Crematogaster sewellii
 * Crematogaster tricolor

Crematogaster hova group
Based on Blaimer (2010, 2012c) - This group of species from Africa and Madagascar includes newly described ants and some members of the synonymized subgenus Decacrema.

1. Antennae 10-segmented (vs. 11-segments in most other species).

2. Petiole broadly or moderately flared, suboval or hexagonal.

3. Postpetiole bilobed, with a more or less distinct median impression.

Molecular and morphological data strongly support the monophyly of this group. These ants are found throughout all forest habitats within the five biomes on the island. Nesting habits are arboreal except for one species that is known to occasionally nest on the ground and is adapted to drier habitats. Many of the canopy-nesting species construct carton nests around small branches or attached to tree trunks, or alternatively nest in dead branches or twigs. It is unclear whether these nesting habits are species-specific. Malagasy hova-group species are medium to large-sized ants compared to other Crematogaster species in this region, and they often seem to be the dominant element of the Crematogaster, or even of the entire canopy ant fauna where they occur. Partly this may be mediated by the carton-nesting ability that allows for large and often polydomous colonies. Carton nesters often tend and house mealybugs in the main nest or in special carton shelters, and both twig- and carton-nesting species can further be found living in association with myrmecophilous beetles (Blaimer, pers. observ.).

Key to Crematogaster hova-group of Madagascar


 * Crematogaster ensifera
 * Crematogaster grevei
 * Crematogaster hova
 * Crematogaster liengmei
 * Crematogaster mahery
 * Crematogaster malala
 * Crematogaster nosibeensis
 * Crematogaster sabatra
 * Crematogaster schencki
 * Crematogaster sisa

Crematogaster kneri group
Blaimer (2012c)

This group will probably contain a large part of the former subgenus Sphaerocrema, but this remains to be tested.

1. Petiole moderately to sharply flared, or suboval.

2. Postpetiole globular, with at most weak posterior impression.

3. Pronotum often with angular or tuberculate lateral margins.

4. Mesonotum often postero-laterally angulate or denticulate.


 * Crematogaster bequaerti
 * Crematogaster chlorotica
 * Crematogaster concava
 * Crematogaster kneri
 * Crematogaster luctans

Crematogaster kelleri group
Blaimer (2012c)

Crematogaster kelleri group

Key to Crematogaster kelleri group workers

Crematogaster scutellaris group
Blaimer (2012c)

1. Petiole moderately to broadly flared, rarely suboval.

2. Postpetiole bilobed, with distinct median longitudinal impression (e.g. Figs 14b & 15b); rarely only with faint impression and postpetiole indistinctly bilobed.

It seems likely that all of the (non-Orthocrema) Nearctic and Palaearctic taxa belong to this clade, as well as a few members of the subgenus Crematogaster that have entered the margins of the northern Neotropics.


 * Crematogaster coarctata
 * Crematogaster ionia
 * Crematogaster isolata
 * Crematogaster lineolata
 * Crematogaster marioni
 * Crematogaster opaca
 * Crematogaster pilosa
 * Crematogaster scutellaris

Crematogaster rogenhoferi group
Blaimer (2012c)

1. Petiole sharply or broadly flared, often with sharp dorsolateral margin.

2. Postpetiole bilobed, with a broad median longitudinal impression.

3. Pronotum with acute or angular margins).

4. Mesonotum convex and posterolaterally margined.


 * Crematogaster flava
 * Crematogaster laeviceps
 * Crematogaster ochracea
 * Crematogaster rogenhoferi

Crematogaster irritabilis group
Blaimer (2012c)

1. Petiole hexagonal, suboval, or elongate-rectangular.

2. Postpetiole varying from narrowly bilobed with sharp but narrow median impression, to strongly bilobed with broad median impression.

3. Pronotum laterally rounded or subangular.

4. Mesonotum in lateral view rounded, and without distinct posterior face.

5. Fairly abundant erect pilosity over entire body.

6. Propodeal spines, if present, often with a downward curve.


 * Crematogaster irritabilis
 * Crematogaster obnigra
 * Crematogaster polita
 * ''Crematogaster treubi
 * + several unidentified / undescribed species.

subgenus Crematogaster Austro-Asian clade species-groups
Includes former members of subgenera Crematogaster sensu stricto (in part), Decacrema (in part), Paracrema, Physocrema and Xiphocrema.

1. Petiole shape in dorsal view circular (Fig. 21a, figures at end of page), oval (Fig. 18a), suboval (Fig. 19a), or greatly flared (Fig. 17a).

2. Postpetiole usually globular, with at most faint posterior impression (Figs 24–25); less commonly postpetiole bilobed (Fig. 17b).

Crematogaster borneensis group
Blaimer (2012c), Feldhaar et al. (2016)

1. Antennae 10-segmented.

2. Head shape rectangular, longer than wide.

3. Petiole in dorsal view suboval, circular or hexagonal.

4. Postpetiole globular, a faint posterior impression may be present.

Most members of this group are obligate inhabitants of Macaranga plants.


 * Crematogaster borneensis
 * Crematogaster captiosa
 * Crematogaster claudiae
 * Crematogaster decamera
 * Crematogaster hullettii
 * Crematogaster linsenmairi
 * Crematogaster maryatii
 * Crematogaster roslihashimi

Crematogaster inflata group
Blaimer (2012c)

1. Members either with propodeum greatly inflated, or posterolateral denticles on the mesonotum.

2. Head large and broad, often medially depressed.

3. Petiole elongate-rectangular, oval or circular.

4. Postpetiole of globular shape, a faint posterior impression may be present.

This group most likely includes members of the former subgenera Physocrema and Paracrema (as listed by Bolton, 2011), as well as probably a number of species that have previously been associated with the subgenus Crematogaster sensu stricto.

You can read details about the subgenus Physocrema and its species. There is also a a key to Physocrema species.

Definitive membership of species in the inflata group is difficult to assess at this point and only certain for the following:


 * Crematogaster ampullaris
 * Crematogaster inflata
 * Crematogaster modiglianii
 * Crematogaster onusta
 * Crematogaster subcircularis

Crematogaster rothneyi group
Hosoishi & Ogata (2019)

The Crematogaster rothneyi group can be distinguished from other Asian Crematogaster species by the following characters:

(1) mandible with four teeth;

(2) 3-segmented antennal club;

(3) a deep metanotal groove;

(4) developed propodeal spines;

(5) petiole broader anteriorly;

(6) bilobed postpetiole with distinct longitudinal median sulcus;

(7) punctuated mesosoma;

(8) stout body setae.

This species group is similar to Crematogaster coriaria in having features (3), (4), (5) and (7), but can be distinguished from Crematogaster coriaria by having features (1), (2), (6) and (8) (Hosoishi and Ogata 2015).


 * Crematogaster rothneyi
 * Crematogaster rothneyi haputalensis
 * Crematogaster yaharai

Crematogaster tetracantha group
Blaimer (2012c)

1. Pronotum antero-laterally with distinct sharp margins or denticles or spinose protuberances.

2. Petiole in dorsal view either greatly flared and transversely convex, or suboval.

This group comprises all members of the previous subgenus Xiphocrema and some additional species from Crematogaster.


 * Crematogaster abrupta
 * Crematogaster dahlii
 * Crematogaster elegans
 * Crematogaster elysii
 * Crematogaster flavitarsis
 * Crematogaster recurva
 * Crematogaster tetracantha
 * Crematogaster weberi

Crematogaster fraxatrix group
Hosoishi and Ogata (2014) - two new species similar to Crematogaster fraxatrix collectively form the Crematogaster fraxatrix group, which occurs in southeast Asia.


 * Crematogaster chhangi
 * Crematogaster fraxatrix
 * Crematogaster simboloni

Crematogaster popohana group
Hosoishi and Ogata (2015) - Crematogaster popohana, and its subspecies known only from the type queens and males, plus one new species form the Crematogaster popohana group. Occuring in southeast Asia, the group can be distinguished from other Asian Crematogaster species by a slender petiole with weakly convex sides.


 * Crematogaster fumikoae
 * Crematogaster popohana
 * Crematogaster popohana amia

Nomenclature

 *  CREMATOGASTER [Myrmicinae: Crematogastrini]
 * Crematogaster Lund, 1831a: 132. Type-species: Formica scutellaris, by subsequent designation of Bingham, 1903: 124.
 * ACROCOELIA [junior synonym of Crematogaster (Crematogaster)]
 * Acrocoelia Mayr, 1853a: 147. Type-species: Acrocoelia ruficeps (junior synonym of Formica scutellaris), by subsequent designation of Wheeler, W.M. 1911f: 158.
 * Acrocoelia junior synonym of Crematogaster: Mayr, 1863: 404; Wheeler, W.M. 1911f: 158; Wheeler, W.M. 1922a: 828.
 * Acrocoelia revived from synonymy as subgenus of Crematogaster: Emery, 1922e: 140.
 * Acrocoelia junior synonym of Crematogaster: Buren, 1959: 126.
 * Acrocoelia revived from synonymy as genus: Soulié, 1964: 398.
 * Acrocoelia junior synonym of Crematogaster: Brown, 1973b: 178; Blaimer 2012: 52. [The type-species of Acrocoelia and Crematogaster are synonymous, the generic synonymy is therefore absolute.]
 * ATOPOGYNE [junior synonym of Crematogaster (Crematogaster)]
 * Atopogyne Forel, 1911d: 343 [as subgenus of Crematogaster]. Type-species: Crematogaster (Atopogyne) hellenica, by subsequent designation of Wheeler, W.M. 1911f: 159.
 * [Type-species not Crematogaster depressa, unjustified subsequent designation by Emery, 1912d: 272; this error repeated in Emery, 1922e: 154 and in Soulié, 1965: 78.]
 * Atopogyne raised to genus: Soulié, 1964: 398.
 * Atopogyne junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Atopogyne subgenus of Crematogaster: Bolton, 1995b: 21.
 * Atopogyne junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * COLOBOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Colobocrema Wheeler, W.M. 1927f: 31 [as subgenus of Crematogaster]. Type-species: Crematogaster (Colobocrema) cylindriceps, by monotypy.
 * Colobocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Colobocrema subgenus of Crematogaster: Bolton, 1995b: 24.
 * Colobocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * DECACREMA [junior synonym of Crematogaster (Crematogaster)]
 * Decacrema Forel, 1910a: 18 [as subgenus of Crematogaster]. Type-species: Crematogaster schencki, by subsequent designation of Wheeler, W.M. 1911f: 161.
 * [Decacrema also described as new by Forel, 1910f: 9.]
 * Decacrema raised to genus: Soulié, 1964: 398.
 * Decacrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Decacema subgenus of Crematogaster: Bolton, 1995b: 26.
 * Decacema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 52.
 * [ Decracrema Arnold, 1920a: 547, incorrect subsequent spelling.]
 * NEMATOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Nematocrema Santschi, 1918d: 182 [as subgenus of Crematogaster]. Type-species: Crematogaster stadelmanni, by original designation.
 * Nematocrema raised to genus: Soulié, 1964: 398.
 * Nematocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Nematocrema subgenus of Crematogaster: Bolton, 1995b: 38.
 * Nematocrema junior synonym of Oxygyne: Blaimer, 2012: 249.
 * Nematocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * OXYGYNE [junior synonym of Crematogaster (Crematogaster)]
 * Oxygyne Forel, 1901e: 375 [as subgenus of Crematogaster]. Type-species: Crematogaster (Oxygyne) daisyi, by subsequent designation of Wheeler, W.M. 1911f: 169.
 * Oxygyne raised to genus: Soulié, 1964: 398.
 * Oxygyne junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Oxygyne subgenus of Crematogaster: Bolton, 1995b: 40.
 * Oxygyne senior synonym of Nematocrema: Blaimer, 2012: 249.
 * Oxygyne junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 52.
 * PARACREMA [junior synonym of Crematogaster (Crematogaster)]
 * Paracrema Santschi, 1918d: 182 [as subgenus of Crematogaster]. Type-species: Crematogaster spengeli, by original designation.
 * Paracrema raised to genus: Soulié, 1964: 398.
 * Paracrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Paracrema subgenus of Crematogaster: Bolton, 1995b: 41.
 * Paracrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * PHYSOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Physocrema Forel, 1912f: 220 [as subgenus of Crematogaster]. Type-species: Crematogaster inflata, by subsequent designation of Wheeler, W.M. 1913a: 82.
 * Physocrema raised to genus: Soulié, 1964: 398.
 * Physocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Physocrema subgenus of Crematogaster: Bolton, 1995b: 42.
 * Physocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * SPHAEROCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Sphaerocrema Santschi, 1918d: 182 [as subgenus of Crematogaster]. Type-species: Crematogaster kneri, by original designation.
 * Sphaerocrema raised to genus: Soulié, 1964: 398.
 * Sphaerocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Sphaerocrema subgenus of Crematogaster: Bolton, 1995b: 46.
 * Sphaerocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * XIPHOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Xiphocrema Forel, 1913k: 80 [as subgenus of Crematogaster]. Type-species: Crematogaster tetracantha, by subsequent designation of Emery, 1922e: 138.
 * Xiphocrema raised to genus: Soulié, 1964: 398.
 * Xiphocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Xiphocrema subgenus of Crematogaster: Bolton, 1995b: 50.
 * Xiphocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.

Blaimer (2012) provides the following diagnostic definition for this globally distributed subgenus:

1. Petiole shape (in dorsal view) highly variable: moderately flared (Fig. 14a), broadly flared (Fig. 15a), sharply flared (Fig.16a), greatly flared (Fig. 17a), oval (Fig. 18a) or suboval (Fig. 19a), elongate rectangular (Fig. 20), circular (Fig. 21a), or hexagonal (Fig. 22a), but not rectangular or ovo-rectangular (as in Fig. 3 or 4). If petiole elongate-rectangular (Fig. 20) and thus similar to some Orthocrema species (as in Fig. 5), then propodeal spiracle compressed oval.

2. Petiole with dorsoposterior denticles/tubercules and dorsoposterior erect setae (e.g. Figs 14a, 16a) or lacking denticles/tubercules (e.g. Figs 15a, 18a–19a, 20, 22a), while setae may still be present.

3. Postpetiole varying from distinctly (Figs 16b-17b, 19b, 22b) to weakly bilobed (Figs 14b–15b, 18b), with a broad (Fig. 16b) to thin median longitudinal impression (Fig. 23). More rarely postpetiole only with faint posterior impression (Figs 18b, 25) or lacking impression entirely (Fig. 24). Probably ~80% of the species diversity in this clade has a clearly bilobed postpetiole with a distinct median longitudinal impression.

4. Propodeal spiracle often oval or compressed oval (Fig. 26).

5. Occipital carinae variable, but often reduced (Fig. 27).

6. Antennae usually 11-segmented, rarely 10-segmented or (one species) 9-segmented. Antennal scapes of variable length; if antennae distinctly clubbed, then usually club 3-segmented.

7. Head shape highly variable, but often with a straight (Fig. 28) or medially depressed posterior head margin (Fig. 29) and with suboval or subangular corners.