Perennial; stems 65-95 cm tall, branched apically, striate, puberulous, branches slender. Lower cauline leaves thin, 14-24 cm long including petiole, petiole 4-9.5 cm long, blade 6.5-7 cm long, lyrate-pinnatipartite, lateral segments 2 pairs, oblong, apex acute to acuminate, terminal segments rhomboid, acuminate, margins mucronulate-denticulate, minutely puberulous on both surfaces; median cauline leaves remote, 9-13 cm long, oblong to lyrate-pinnatifid, apex acuminate, narrowed at base into winged petiole; upper leaves gradually smaller, lanceolate to linear, sessile. Inflorescence paniculate; heads nodding in bud; involucre cylindric, glabrous, purple, 12×3-4 mm; bracteoles ovate-oblong, basal, outer bracts 2-seriate, outer ones oblong, 2 mm long, inner ones linear-oblong, 5-6 mm long, inner bracts 5, linear. Florets 5; corolla purple, 11 mm long, deeply 4-lobed. Achenes reddish purple, fusiform, 4-5×1 mm, compressed, 7-9-grooved. Pappus white, 8-9 mm long, bristles subequal.

ILAN: Taipingshan to Tulishan, Wang et al. 9348. TAOYUAN: Lalashan, Peng 14607. NANTOU: Yunhai to Tienchih, Liu 6. CHIAYI: Alishan, Peng 6021. KAOHSIUNG: Tengchih to Shihshan, Ohashi et al. 23640. HUALIEN: Mukuashan, Peng 7289.

Endemic; mountains, 1,500 to 2,500 m.

Notoseris formosana closely resembles Paraprenanthes sororia in foliage and habit, differing in the longer involucral bracts in ±3 series, more compressed and truncate achenes and in the longer pappus.