This member of the RUBIACEAE family was described by William Jack in 1823. It's found in the jungles in Cambodia,Thailand, Vietnam and Malaysia. It's a epiphyte, and needs a lots of moist, but not much sun. It can be reproduced both by cuttings and seeds. The caudex will get op to 30 centimetres, the branches 40 centimetres.
The caudex is hollow, and forms a perfect nest for the ants, which protect the plant, and gets home and sweet sap in exchange. It get a lots of white small flowers, and small red fruits.H. formicarum, have 6-12 pairs of veins in their leathery leaves, brownish and rough caudex with ridges, ant entrances only along the soil line, flowers 3-4 millimetres.
It is considered by Dr C. R. Huxley to be an ochlospecies, which simply means a species that is so variable, it has not been possible to define population parameters. That seems obviously, when the plants from Cambodia was found.