Description from Flora of China
Ophioglossum japonicum Thunberg in Murray, Syst. Veg., ed. 14, 926. 1784; Hydroglossum japonicum (Thunberg) Willdenow; Lygodium chaerophylloides Desvaux; L. cochinchinense Desvaux; L. dissectum Desvaux; L. japonicum var. microstachyum (Desvaux) C. Christensen & Tardieu; L. microstachyum Desvaux; L. microstachyum var. glabrescens Nakai; L. pubescens Kaulfuss.
Rhizome widely creeping, dichotomously branched, 2-5 mm in diam., densely clothed with dark brown hairs, fronds commonly 5-10 mm apart. Juvenile fronds erect, first branching an unequal dichotomy (?always), two main branches of large fronds bipinnate, deltoid in outline, with palmatisect pinnae, pinna margins doubly serrate. Rachis of climbing fronds hardly ca. 2 mm in diam., glabrous except for minute hairs on flattened adaxial surface between narrow wings; primary rachis branches 3-10 mm, dormant apex covered with pale hairs; secondary branches of fronds on young or stunted plants pinnate, on well-grown fronds bipinnate or tripinnate, deltoid in outline, commonly ca. 12 cm long and wide, rachises densely shortly hairy on adaxial surface and with fewer longer hairs elsewhere; sterile tertiary pinnae of lower rachis branches palmate with 5-7 lobes, middle lobe much longer than lateral lobes, tertiary pinnae higher up frond 3-lobed with an elongate middle lobe or pinnate with small oblique and often lobed quaternary pinnae and a usually deltoid-pinnatisect terminal pinna ca. 3 cm, margins acutely biserrate, apex obtuse or subacute; stalks of pinnae up to 3 mm, never articulate or thickened at apex; costae usually with long scattered hairs, veins and surfaces usually glabrous but sometimes shortly hairy; fertile secondary branches tripinnate, pinnae smaller than sterile pinnae, sorophores 2-12 mm; indusia glabrous or with few hairs if lamina hairy; spores finely low tuberculate to verrucose with prominent laesurae.
Climbing in secondary vegetation; sea level to ca. 500 m (in Taiwan). Anhui, Chongqing, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hainan, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shanghai, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Bhutan, India, Indonesia (Java), Japan, Kashmir, Korea, Nepal, Philippines, Sri Lanka; tropical Australia, North America].