Several phragmotic species in the ant genus Carebara Westwood, 1840 with a cephalic shield are known from the Old World, but species with an anteriorly truncated head seem to be unknown until now. A new species, resembling the phragmotic workers of the ant genus Colobopsis, is here described as Carebara colobopsis Hosoishi & Yamane, sp. nov., based on major and minor worker found in Cambodia. This new species is similar to Carebara acutispina (Xu) and C. obtusidenta (Xu) in some important characters, but distinguished from the latter two by distinct metanotum and deep groove in front of metanotal disc in the major worker, and longer head and deep metanotal groove in the minor worker. This is the first confirmed record of a truncated phragmotic head in the major worker of the genus Carebara. We propose the Carebara acutispina species group to include all the three species, present a diagnosis of this group, and provide a key to species based on the major and minor worker castes.

The myrmicine genus Rotastruma is a rarely collected arboreal ant group and only two species, R. recava Bolton and R. stenoceps Bolton, are known from the Oriental Region. A new species, R. epispinasp. nov., is described from Cambodia based on the worker and queen castes. The new species is distinguished from R. recava and R. stenoceps by having the propodeal spine directed upwards and elongated peduncle of the petiole. Herein, we provide an update to the identification key and diagnostic characters for the genus Rotastruma.

A recent molecular phylogeny of the genus Crematogaster reclassified some members of the former subgenera Paracrema and Physocrema into the C. inflata-group, now comprised of five species: C. ampullaris, C. inflata, C. modiglianii, C. onusta and C. subcircularis. Here, a molecular analysis of the Crematogaster inflata-group and eight other species of the former subgenus Physocrema (C. aurita, C. difformis, C. mucronata, C. physothorax, C. sewardi, C. tanakai, C. vacca and C. yamanei) is conducted using a total of c. 4 kb of sequence data from six nuclear protein-coding genes and two mitochondrial genes. Monophyly of the C. inflata-group is strongly supported. A revised morphological delineation of the subgroups is proposed, supported by the molecular phylogeny: three morphologically distinct subgroups, the C. difformis-subgroup, the C. vacca-subgroup and the C. inflata-subgroup. Molecular dating and biogeographical analyses indicate that the C. inflata-group originated in the Sundaic region around the Middle Miocene 12 Mya and diversified from the Late Miocene to Pliocene. Ancestral state reconstructions indicate that the C. inflata-group diversified from an ancestor with a swollen propodeum and circular-shaped metapleural gland opening. Biogeographical reconstruction indicates that dispersal to peripheral areas and allopatry due to sea-level changes shaped the evolutionary history of the C. inflata-group.