Ophioglossum angustatum Maxon, nom. illeg. superfl.; O. japonicum Prantl (1883), not Thunberg (1784); O. nipponicum Miyabe & Kudô; O. savatieri Nakai, nom. illeg. superfl.; O. thermale var. nipponicum (Miyabe & Kudô) M. Nishida ex Tagawa; O. vulgatum Linnaeus var. thermale (Komarov) C. Christensen.

Plants 10-20 cm tall. Rhizomes erect, slender, bearing a cluster of unbranched fleshy roots; roots stolonlike, producing new plants at apices. Fronds simple or 2 or 3 together. Common stalk green or pale when lower part buried underground, 3-6 cm, slender. Sterile lamina simple, sessile, light green, oblanceolate or oblong-oblanceolate, 2-5 cm × 3-10 mm, herbaceous, base narrowly cuneate, margin entire, apex slightly acute or obtuse; veins reticulate, indistinct, but visible under light. Sporophore arising from base of sterile lamina; stalk 5-7 cm, overtopping sterile lamina; spike narrowly linear, 2-3 cm, acute at apex, with 15-28 pairs of sporangia. Spores pale, surface subreticulate or subsmooth. 2n = 240-960.

Grassy hillsides, near thermal springs; 200-1800 m. Anhui, Guizhou, Hebei, Heilongjiang, Henan, Jiangsu, Jiangxi, Jilin, Liaoning, Shaanxi, Shandong, Sichuan, E and SE Taiwan, Yunnan [Japan, Korea, Russia (Kamchatka)].