Subshrubs or herbs, perennial, 50-80 cm tall, rhizomatous. Stems erect, simple, stout, flexuous, ± woody at base, purplish, finely striate, strigillose, villosulous, sparsely minutely stipitate glandular, particularly below leaves. Leaves cauline, slightly reduced upward, abaxially pale green, glabrous, veins sparsely strigillose, minutely stipitate glandular, sometimes in pits, adaxially green, densely scabridulous, margin coarsely serrate, ciliate, veins prominent, apex long acuminate, mucronate; lowest leaves withered by anthesis (not seen), broadly winged petiolate, lanceolate, ca. 22 cm, base attenuate, apex acuminate; lower leaves (not seen) to upper leaves shortly broadly winged petiolate (base clasping) or sessile, lanceolate, (5-)6-17 × 1.5-5.5 cm, base attenuate or auriculate, clasping; synflorescence leaves sessile, lanceolate, 0.5-6 × 0.1-1.2 cm, base auriculate, clasping, margin serrate to serrulate, rapidly becoming bracts. Capitula 10-45 or more, in terminal corymbiform synflorescences, 10-12 mm in diam.; peduncles 6-50 mm, densely strigillose; bracts linear-lanceolate, entire. Involucres campanulate, 4-4.5 mm; phyllaries 2- or 3-seriate, subequal, sometimes squarrose, green distally, oblanceolate to lanceolate or linear-lanceolate (inner phyllaries), 3.5-4.5 × 0.5-1 mm, abaxially sparsely strigillose, mainly on veins, sparsely to moderately minutely stipitate glandular, margin scarious to narrowly scarious, erose, sparsely ciliate, midvein more pronounced distally, ± translucent, apex acuminate, purplish, sparsely ciliate. Ray florets 30-35(-60), white, rose, blue, or purple, tube apex sparsely stipitate glandular, lamina 4-5 × ca. 1 mm, glabrous; disk florets yellow, becoming purplish, 3.5-4 mm, tube base flared, limb campanulate, ca. 2 mm, glabrous, proximally sparsely stipitate glandular, lobes spreading, narrowly triangular, 0.8-1 mm, purplish. Achenes obovoid, slightly compressed, ca. 2.2 mm, sparsely strigillose, eglandular, 4-ribbed. Pappus 2- or 3-seriate, brownish; outer bristles 0-2, slender, 1.5-2 mm; inner bristles 2.5-3 mm, acute; innermost bristles 3.5-4 mm, slightly clavate. Fl. Aug-Oct.

Aster sikkimensis is related to A. nigromontanus, but it differs by its finely pubescent phyllaries and leaf shape.

2400-3600 m. S Xizang [India (Sikkim), Nepal].