The commonly traded species has been identified as H. moseleyanum (syn. H. papuanum) and is also almost identical to the species from a Botanical Gardens in Europe collected in 1960s or 1970s from New Guinea. They have matt lime-green semi-succulent leaves and silvery brown tubers. The species from Northern Australia is also similar but is more deciduous under the same cultivation regime. It shreds leaves easily when dry. Finally, 2 species from Irian Jaya looks more intermediate just like the other H. aff. moseleyanum from the Philippines and Bogor, Java. These 2 irian plants differs in having longer pointed leaves.
Maybe it is more practical to define this group as a formicarum-moseleyanum complex rather than to pin a name to it.