12. Asplenium nidus Linnaeus, Sp. Pl. 2: 1079. 1753.
巢蕨 chao jue
Asplenium neohainanense Viane; Neottopteris hainanensis Ching; N. nidus (Linnaeus) J. Smith ex Hooker; N. rigida Fée; N. salwinensis Ching; N. vulgaris J. Smith, nom. illeg. superfl.; Thamnopteris nidus (Linnaeus) C. Presl.
Plants 1-1.2 m tall. Rhizome erect, thick and short, woody, apex scaly; scales dark to purplish brown, narrowly triangular to linear-subulate, margin ciliate to fimbriate. Fronds caespitose; stipe pale brown, up to 5 cm, woody, when dry semiterete abaxially, base densely scaly; lamina lanceolate, 90-120 × (8-) 9-15 cm, gradually decurrent on stipe, base cuneate, margin entire, apex acute to acuminate. Midrib raised and semiterete on upper adaxial side but flat abaxially, subglabrous, grayish to pale brown; veinlets simple or forked, parallel and connected at their apex to marginal vein. Fronds papery or thinly leathery, when dry grayish green, glabrous. Sori linear, 3-5 cm, on acroscopic side of veinlets, running from near their base up to 1/2 of their length; basal part of lamina usually sterile; indusia brownish, linear, thickly membranous, entire, persistent. Spores with lophate (costate to cristate) perispore. Plants sexual tetraploid: 2n = 144.
Clustered on tree trunks or rocks in rain forests; 100-1900 m. ?Guangdong, Guangxi, Guizhou, Hainan, Taiwan, Xizang, Yunnan [Cambodia, India, Indonesia, Japan, Laos, Malaysia, Myanmar, Sri Lanka, Vietnam; tropical regions of E Africa and Australia, Pacific islands (Polynesia)].
Asplenium nidus is accepted here in a broad sense and constitutes a species complex (e.g., Murakami et al. in M. Kato, Biol. Biodivers. 53-66. 1999; Yatabe et al., Amer. J. Bot. 88: 1517-1522. 2001). The variability of its frond and perispore morphology (e.g., Wei & Dong, Nordic J. Bot. 30: 90-103. 2012), as well as other phenetic characters, is not well studied in relation to its molecular diversity.
Asplenium setoi N. Murakami & Serizawa, recently described from Japan, might be present at low elevations in China (Taiwan); typical specimens can be distinguished from A. nidus by their keeled to boat-shaped midrib. Another species regularly confused with both A. setoi and A. nidus is the often cultivated A. australasicum (J. Smith) Hooker, a South Pacific taxon.
Based on their particular venation pattern, taxa resembling Asplenium nidus have been recognized as a separate section (A. sect. Thamnopteris Hooker & Baker), a subgenus (A. subg. Thamnopteris C. Presl), or as a genus of its own (Neottopteris J. Smith; syn. Thamnopteris (C. Presl) C. Presl). Plants are often epiphytes with large simple fronds growing in a close spiral and forming the typical birds nest. Veins departing from the midrib (rachis) fork anadromously, run almost parallel and straight to the margin where they connect to a common submarginal vein. However, recent molecular studies do not support the separation of this group as a separate genus. The clade consists of 15-30 species, and modern research shows that more taxa may await description. A critical revision of the group is urgently needed. Members occur mainly in rain forests of tropical Asia and the Pacific. A few taxa are widely cultivated as house plants and sold as "birds-nest fern." Many plants in commerce belong to A. australasicum, which can be distinguished from true A. nidus by its abaxially dark brown carinate midrib.