半月形铁线蕨 ban yue xing tie xian jue

Adiantum arcuatum (Poiret) Swartz; A. lunatum Cavanilles; A. lunulatum N. L. Burman; A. lunulatum var. limbatum Christ; A. lunulatum var. subjunonicum Christ; Polypodium arcuatum Poiret; Pteris lunulata (N. L. Burman) Retzius.

Plants terrestrial or epilithic, 10-50 cm tall. Rhizomes erect, short, scales dark brown, lanceolate, margins denticulate. Fronds clustered; stipe castaneous, glossy, 6-25 cm, terete, base with same scales as rhizome, distally glabrous; lamina 1-pinnate, lanceolate in outline, 12-25 × 2-6.5 cm; rachis, costae, and stalks same color as stipe, apex usually prolonged into a whiplike stolon and rooting to form new plantlets; pinnules 6-12 pairs, alternate, obliquely spreading; stalk 10-20 mm, articulate, persistent after pinnules fall; blade below middle subequal in size, dimidiate-lunate or semi-orbicular-reniform, 1-4 × 1-2.3 cm, herbaceous, green or brown-green, both surfaces glabrous, upper margin rounded, apex obtuse or bent downward, sterile pinnules stalked, both sides asymmetrical; margins undulate-lobed, segments obtuse and serrulate at apex, lower margins entire, truncate or slightly bent downward, rarely broadly cuneate, fertile pinnules subentire or with 2-4 shallow sinuses, or slightly undulate; distal pinnules slightly smaller; terminal pinnules flabellate, slightly larger than basal pinnules; veins multidichotomously forked and reaching margins, visible on both surfaces. Sori 2-6 per pinna; false indusia dark brown or brown-green, linear-oblong, membranous, upper margins flat and straight or slightly depressed, entire, persistent. Perispore finely granular.

Gregarious on shaded wet places or on acidic soil in forests, sometimes rupicolous; 100-2000 m. Guangdong, Guangxi, Guizhou, Hainan, Sichuan, Taiwan, Yunnan [Bhutan, India, Indonesia, Kashmir, Malaysia, Myanmar, Nepal, Philippines, Thailand, Vietnam; tropics and subtropics of Africa, Oceania].

There has been controversy as to the correct name of this taxon. Pichi Sermolli (Webbia 12: 665. 1957) lectotypified Adiantum philippense with the illustration "Adiantum Philippense, folio rotundo laciniato" in Petiver (Gazophyl. Nat., 8, t. 4, f. 4, 1702-1709). Some (e.g., Morton in Contr. U. S. Natl. Herb. 38: 370. 1974; Verdcourt, Fl. Trop. East Africa: 58. 2002) have argued that this illustration is unidentifiable and might not even be a fern. Fraser-Jenkins (Taxon. Revis. Indian Subcontinental Pteridophytes, 144. 2008) claims that Petiver’s drawing was copied from a drawing sent to him by Kamel and that the original drawing and herbarium material upon which it was based are available in the Sloane Herbarium (BM) and prove that A. philippense is indeed this species. Verma and Fraser-Jenkins (in S. C. Verma, S. P. Khullar & Cheema, Perspec. Pterido. 82-83. 2009, fidé Fraser-Jenkins, loc. cit.) recognized two further subspecies: the diploid sexual subsp. teestae S. C. Verma & Fraser-Jenkins in which they included Chinese material, the diploid and tetraploid apomictic subsp. intermedium S. C. Verma & Fraser-Jenkins, and epitypified subsp. philippense with material of a known triploid apomict from India.

Adiantum philippense is an indicator of acidic conditions, as it grows in soils of pH 4.5-5.