Herbs perennial, 35-45 cm tall; rhizomes robust (to 6 mm in diam.); roots dense, fibrous, bearing rosulate phyllome. Stems single, erect, stout (5-7 mm in diam.), purple-red above, angled and finely canaliculate, hirsute (hairs ca. 4 mm) below, densely leafy below, densely pilose above. Leaves: both surfaces densely pilose, margin hirsute-ciliate, midvein stout, hirsute, abaxially triplinerved, veins prominent, lateral veins fine; basal leaves withered or present at anthesis, broadly winged petiolate; blade oblong-spatulate, 7-12 cm, base attenuate, margin subentire toward middle, apex obtuse or rounded; middle cauline leaves sessile, oblong or oblong-lanceolate, smaller, apex obtuse or acute. Capitula terminal, solitary, ca. 6.5 cm in diam. Involucres hemispheric, ca. 2 cm in diam.; phyllaries 3-seriate, squarrose, oblong or linear-lanceolate, ca. 10 × 1.5-2 mm, leaflike, base hardened, outer phyllaries densely hirsutulous, inner phyllaries pilose distally, margin ± reddish, apex obtuse or ± acute. Ray florets ca. 100, purple-red, lamina 25-30 × ca. 3.4 mm; disk florets yellow, ca. 6 mm, sparsely hairy. Achenes (immature) ± compressed, ca. 2 mm, densely strigose. Pappus purplish brown, of few unequal bristles, barbellate throughout, bristles shorter than disk florets. Fl. Aug.

Aster megalanthus is closely related to A. tongolensis but differs by being taller and in having more ray florets with broader laminae and longer disk florets.

● Slopes; ca. 4000 m. W Sichuan (Zhegu Shan).