Monomorium rosae is a widely distributed species with a central African distribution that stretches from Kenya to Senegal. It was collected twice on Jinack Island in The Gambia, once on a tree and once in dry leaf litter at the base of a tree.
Bolton (1987) notes that this species varies in size and pilosity over its range, suggesting that M. rosae may contain more than one species. He distinguishes the species as currently defined as having 11-segmented antennae, dark colour, moderately long scapes and a distinctively shaped postpetiole.
It's interesting how many of the Monomorium now known from The Gambia have 11-segmented antennae. M. dolatu, M. exiguum, M. mictilis and M. rosae all have 11-segmented antennae, out of ten species recorded from The Gambia (40%). This contrasts with 12 species out of 149 listed by Bolton for Africa as a whole (8%). Maybe Monomorium with 11-segmented antennae are more common in this part of west Africa?
These have been compared with specimens checked by Bolton at the Natural History Museum, London, and are confirmed as M. rosae.