Inula is a large genus of about 90 species of flowering plants in the family Asteraceae, native to Europe, Asia and Africa. Inula japonica Thunberg, Herbs, perennial, from short rhizomes. Stems 15-100 cm tall, striate, appressed pilose, sometimes glabrescent, simple, branched up to synflorescence. Leaves radical and cauline; radical and lower cauline leaves smaller than median leaves, withering before flowering; median leaves lanceolate, oblong, or ovate, appressed pilose or subglabrous on both surfaces, base abruptly narrowed, sessile or semiclasping, apex subacute; upper leaves gradually smaller, 10-25 mm. Capitula usually few or solitary, radiate, ca. 3.5 cm in diam., sometimes with subtending bracteal leaves. Eight new dimeric sesquiterpene lactones (japonicones E-L, 1- 8), including a novel sesquiterpene dimer bearing a rare hydroperoxide group (japonicone E, 1), were isolated from the aerial part of Inula japonica Thunb.