Description from Flora of China
Begonia longiciliata C. Y. Wu.
Herbs, to 40 cm tall. Rhizomes elongate, 7-14 mm in diam. Leaves basal; stipules caducous, 1.4-1.5 × 1.6-1.8 cm, membranous; petiole to 35 cm, densely long hirsute; blade abaxially purplish, adaxially dark green with a grayish green or silver horseshoe-shaped spot, ovate to narrowly ovate, asymmetric, 6-33 × 5-21 cm, abaxially sparsely hairy, adaxially long setose, venation palmate, 6- or 7-veined, base oblique, cordate, margin serrulate and ciliate, apex shortly acuminate. Inflorescences 10-13 cm tall, subglabrous. Staminate flowers: pedicel 2.2-3.5 cm; tepals 4, pinkish to pink, glabrous, outer 2 oblong-ovate, 1.3-2 cm × 8-17 mm, apex obtuse to acute, inner 2 oblong-lanceolate, 0.9-1.8 cm × 3.5-8 mm; stamens 100-120; filaments 2-5.4 mm; anthers oblong, 1.3-2.9 mm, apex acuminate. Pistillate flowers: pedicel 2.9-3.1 cm; tepals 5, unequal, elliptic to broadly ovate, glabrous, largest ca. 2 × 1.5-1.7 cm, smallest 1.6-1.8 cm × 6-8 mm, apex acute to obtuse; ovary glabrous, 2-loculed; placentae axile, bilamellate; styles 2, free, 4.4-5.2 mm; stigmas 2-cleft, spiraled. Capsule nodding, unequally 3-winged; abaxial wing ligulate or falcate, 1.5-2.5 cm, apex rounded; lateral wings lunate, 3.5-5 mm. Fl. May, fr. Aug. 2n = 22*.
Begonia sizemoreae Kiew (Gard. Bull. Singapore 56: 95. 2004), described from Vietnam, definitely belongs to the same complex as B. rex, but the distinction between the two species awaits further study.
Forests, on rocks and in caves in valleys; 400-1100 m. Guangxi, Guizhou, Yunnan [NE India, Vietnam].