Humulus japonicus.Early Detection & Distribution Mapping Service.edd.mapps.org (Accessed 6/2015).

Humulus japonicus is an annual vine; stem green, stout, very rough. 

Leaves opposite, palmately 5-9 lobed, upper blades 3-5 lobed, hairy, very rough, rather irritating, petiole longer than blade, major veins palmate, secondary veins pinnate, superficially like a vine of Cucurbitaceae but opposite and with more lobes. 

Flowers greenish, inconspicuous, dioecious (sexes on different plants), female flowers in short spikes above leaf-like bracts, flower bracts less than 1 cm, spiny-hairy, no petals, ovary enclosed in entire, papery calyx. 

Fruit dry, small, one-seeded (achene), surrounded by persistent calyx; blooming and fruiting July-Oct. 

Wetland status: FACU. 

Frequency in NYC: Infrequent. 

Origin: Asia. 

Habitat: Edges, roadsides, moist part shade. 

Humulus japonicus.female flowers.© Shigenobu Aoki.nature.jardin.free.fr (Accessed 6/2015).

Notes: Very aggressive and fast growing. Sometimes introduced with root balls of nursery plants (personal observation). Host to larvae of the question mark butterfly, Polygonia interrogationis (Nymphalidae), (Tallamy 2003; Pyle 1981).