Description from Flora of China
Plants terrestrial, evergreen, erect, (20-)50-70 cm, with creeping subterranean rhizome and stolons. Rhizophores restricted to base of stem or to creeping rhizomes and stolons. Main stems branched from middle upward, a few lower branches abortive, pinnately branched, stramineous, unbranched main stem 20-30 cm tall, main stem 3-5 mm in diam. at lower part, subquadrangular, sulcate, glabrous; primary leafy branches 3-7 pairs, once or twice pinnately branched, secondary branches forked, branchlets dense, adjacent primary branches on main stem 2.5-9 cm apart, leafy main stem including leaves 10-14 mm wide at middle, ultimate branches 5-8(-10) mm wide including leaves. Axillary leaves on branches symmetrical, triangular or ovate-lanceolate, 3.2-5 × 1.1-1.8(-2.3) mm, base deeply cordate or subcordate, or slightly biauriculate, margin long ciliolate at base, margin elsewhere shortly ciliolate. Dorsal leaves contiguous or imbricate, asymmetrical, ovate-elliptic, 2.2-2.8(-3.6) × 1-2 mm, strongly carinate, base obliquely cordate, with few long cilia at base, ciliolate upward, apex aristate. Ventral leaves slightly ascending, asymmetrical, oblong-falcate, 4.7-7 × 1.7-2.6 mm, apex acute; acroscopic base rounded, overlapping stem and branches, margin long ciliolate at very base, then shortly ciliolate below middle of leaf, elsewhere entire, cilia 0.2-0.5 mm. Strobili solitary or in pairs, terminal or lateral to branches, compact, tetragonal, 10-45 × 1.8-3 mm; sporophylls unlike sterile leaves, uniform, not white-margined, sharply carinate, margin denticulate, apex acuminate; megasporophylls only 1 in lower portion on lower side, elsewhere with sporophylls, microsporophylls, or megasporophylls and microsporophylls at intervals, or megasporophylls in middle on lower side; microsporangia elliptic-oblong, relatively thick, marginal cells differentiated, smaller with thin walls; microspores light pale yellow, megaspores whitish or gray.
Selaginella superba was treated as a synonym of S. frondosa Warburg but can be distinguished from the latter by the much larger leaves. It is the most beautiful species of the Chinese Selaginella. The main stem is very strong and has a bladelike upper part. It is found only in Hekou, Yunnan, on the border with Vietnam, where the type was collected. The typical form occurs mainly in lowland forests along riverbanks at 100-200 m in elevation, while another form was found only on limestone hills from 300-500 m, in monsoon semi-evergreen rain forests. The two forms differ much in branching patterns and leaf shape and margin. The two forms could be different species, but they share most of the common important characters, e.g., the stem, leaf, strobilus, and spores. Further studies are needed to better ascertain their delimitation.
Rain forests in limestone areas; 100-500 m. S Yunnan [N Vietnam].