Description from Flora of China
Trees; branchlets, petioles, young leaf blades abaxially, rachis of inflorescences, and perianth covered with reddish brown, dusky, or grayish brown, very short, felted puberulence. Petiole 1-1.8 cm; leaf blade obovate, obovate-elliptic, ovate-elliptic, or broadly ovate, 5-12(-17) × 2.5-5(-6) cm, thickly papery to nearly leathery, abaxially often grayish with age, base acute to broadly cuneate, margin serrate except basally entire, apex rounded to mucronate; midvein adaxially impressed but often slightly raised on sprouted branch leaves; secondary veins 10-15(-18) on each side of midvein. Infructescences 10-17 cm; rachis 5-6 mm thick. Cupule 4-5 cm in diam., wall ca. 1 mm thick; bracts spinelike, congested, entirely covering cupule, to 1.5 cm, basally connate. Nut 1 per cupule, broadly conical, 1.2-1.5 × 1.6-2 cm, densely pubescent; scar exceeding base of nut. Fl. Mar-Apr, fr. Aug-Oct of following year.
Could be recognized as an insular subspecies of Castanopsis indica. The status of C. undulatifolia G. A. Fu (Guihaia 14: 301. 1994) is uncertain, but it may be conspecific with C. hainanensis.
* Broad-leaved evergreen forests; below 400 m. Hainan