Petasites tricholobus, Plants subdioecious. Rhizomes short, with numerous fibrous roots, thinly arachnoid-lanate. Scapes emerging from rhizomes in early spring. Stems of female synflorescences 27-60 cm tall, with scale-shaped leaves; bracteal leaves ovate-lanceolate, 3-4 cm, basal leaves long petiolate; blade broadly reniform-cordate, 2-8 cm, both surfaces white lanate, or later ± glabrescent, palmately veined, margin finely toothed, with cartilaginous mucronulate teeth. Male capitula arranged in terminal corymbs or panicles; corolla tubular, segments lanceolate; style exceeding corolla, stigma capitate, slightly branched. Two novel pentacyclic triterpenoids, petatrichol A (1) and petatrichol B (2), along with 10 known compounds, were isolated from the rhizome of Petasites tricholobus, their structures were elucidated by spectroscopic methods. A new bakkenolide-type compound, bakkenolide-Va(1), was isolated from the rhizome of Petasites tricholobus.