24. Adiantum davidii Franchet, Nouv. Arch. Mus. Hist. Nat., sér. 2. 10: 112. 1887.
白背铁线蕨 bai bei tie xian jue
Adiantum aristatum Christ; A. davidii var. aristatum (Christ) C. Christensen; A. davidii var. latedeltoideum (Christ) Ching; A. davidii var. longispinum Ching; A. davidii var. prattii (Baker) C. Christensen; A. latedeltoideum (Christ) C. Christensen; A. monochlamys Eaton var. latedeltoideum Christ; A. prattii Baker.
Plants epilithic, 20-30 cm tall. Rhizomes long creeping, slender, scales dark brown, glossy, lanceolate, margins entire. Fronds spaced apart; stipe dark castaneous, 10-21 cm, with same scales as rhizome, distally glabrous; lamina 3-pinnate, triangular-ovate in outline, 10-15 × 6-10 cm, apex acuminate; pinnae 3-5 each side, obliquely spreading; rachises, costae, and stalks same color as stipes, with brown, multicellular, articulate hairs at base of pinnae and pinnules; basal pair of pinnae largest, 2-pinnate, narrowly triangular in outline, 5-7 × 3-4 cm; pinnules 4 or 5 pairs per pinna, slightly overlapping, obliquely spreading, apex obtuse; stalk castaneous, 1-4 mm, slender; blade uniform in shape, flabellate, 4-7 × 4-7 mm, progressively smaller distally, hard herbaceous, abaxially gray-green, adaxially green or glaucous, both surfaces glabrous, base cuneate, bilateral margins entire, apex rounded, with dense short and broad serrations with short cartilaginous awn points. Veins multidichotomously forked, reaching apices of serrations, visible on both surfaces. Sori 1(or 2) per pinnule, horizontally attached at apical sinus of pinnule; false indusia dark brown, reniform or orbicular-reniform, papery, upper margins shallowly depressed, entire, persistent. Perispore thickly granular. 2n = 240*.
● On rocks by streamsides; 1100-3400 m. Gansu, Guizhou, Hebei, Henan, Shaanxi, Shanxi, Sichuan, Yunnan.