Abh. Math.-Phys. Cl. Königl. Bayer. Akad. Wiss 4(3): 213. 1846.
Herbs, annual, vining, 0.5-2.5 m. Stems usually branched. Leaves: petioles usually longer than blades. Leaf blade cordate, palmately 5-9-lobed, 5-12 cm, margins of lobes serrulate, apex acuminate; surfaces abaxially with veins pubescent, with stiff hairs, glands yellow, sessile, discoid, adaxially margins of younger leaf blades with stiff cystolithic hairs. Inflorescences: staminate inflorescences erect, 15-25 cm, flower anthers without glands; pistillate inflorescences spikes, conelike, ovoid; bracteole ovate-orbiculate, 7-10 mm, pilose, margins densely ciliate-hairy. Infructescences pendulous, green, conelike, ovoid to oblong, (1-)1.5-3(-4) cm; bracteoles without yellow glands. Achenes yellow-brown, ovoid-orbicular, inflated to lenticular, 4-5 mm, glandless. 2n = 20, including 6 chromosomes concerned with sex determination.
Phenology: Flowering early-mid summer.
Habitat: Roadsides, fencerows, waste places, riverbanks
Elevation: 0-1000 m
Introduced; Ont., Que., Ala., Ark., Conn., Del., Ga., Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Nebr., N.J., N.Y., N.C., N.Dak., Ohio, Pa., R.I., S.C., S.Dak., Tenn., Vt., Va., W.Va., Wis., Asia.
Although I have no records from New Hampshire, the state is within the geographic range of Humulus japonicus.
Variegated forms of Humulus japonicus, cultivated as ornamentals, are sometimes spontaneous. The vernacular name Japanese hop(s) is occasionally misapplied to H. lupulus var. cordifolius (Miquel) Maximowicz, a variety not found in North America.
The disposition of the name Humulus scandens (Loureiro) Merrill, based on Antidesma scandens Loureiro, is problematic. E. D. Merrill (1935) was convinced that the name A. scandens applied to the species Humulus japonicus. If Merrill was correct, then the combination Humulus scandens would have priority. The material described by Loureiro, however, was not preserved, and his description does not coincide with that of H. japonicus. Humulus scandens is not included in synonymy in this treatment.
I. A. Grudzinskaya (1988) segregated Humulus japonicus as a new monotypic genus, Humulopsis, with the single species Humulopsis scandens (Loureiro) Grudzinskaya.