After successful laboratory rearing of both males and females from a single clutch of eggs, the genus Nanophyllium Redtenbacher, 1906 (described only from males) and the frondosum species group within Phyllium (Pulchriphyllium) Griffini, 1898 (described only from females) are found to be the opposite sexes of the same genus. This rearing observation finally elucidates the relationship of these two small body sized leaf insect groups which, for more than a century, have never been linked before. This paper synonymizes the frondosum species group with Nanophyllium Redtenbacher, 1906 in order to create a singular and clearly defined taxonomic group. Five species are transferred from the Phyllium (Pulchriphyllium) frondosum species group and create the following new combinations: Nanophyllium asekiense (Größer, 2002), comb. nov.; Nanophyllium chitoniscoides (Größer, 1992), comb. nov.; Nanophyllium frondosum (Redtenbacher, 1906), comb. nov.; Nanophyllium keyicum (Karny, 1914), comb. nov.; Nanophyllium suzukii (Größer, 2008), comb. nov. The only taxon from this species group not transferred from the frondosum species group to Nanophyllium is Phyllium (Pulchriphyllium) groesseri Zompro, 1998. Based on protibial exterior lobes, this species belongs in the schultzei species group as described in Hennemann et al. 2009 and is therefore excluded from further discussion here. The rearing of Nanophyllium also yielded the male Nanophyllium asekiense (Größer, 2002), comb. nov. thus, enabling comparison of this male to the other previously known Nanophyllium species. Two new species of nano-leaf insects are described within, Nanophyllium miyashitaisp. nov., from Morobe Province, Papua New Guinea, and Nanophyllium daphnesp. nov., from Biak Island, Papua Province, Indonesia. With such distinct sexual dimorphism in Nanophyllium between sexes, which have only now been matched up via captive rearing, illustrated within are numerous specimens which might represent the unknown opposite sexes of the many currently known species of Nanophyllium. Due to pronounced sexual dimorphism in Nanophyllium, only future captive rearing or molecular analysis will match up the many unknown sexes. To conclude, with the description of two new Nanophyllium species, dichotomous keys to species for known males and females are presented.
