- Protologue: Gen. fil.: pl. 3 (1834).
- Family: Nephrolepidaceae
- Chromosome number: x= 41;N. biserrata,N. cordifolia: 2n= 82
Major species and synonyms
- Nephrolepis biserrata (Swartz) Schott, Gen. fil.: pl. 3 (1834), synonyms: N. acuta (Schkuhr) C. Presl (1836), N. ensifolia (Schkuhr) C. Presl (1836), N. exaltata (L.) Schott var. biserrata (Swartz) Baker (1870).
- Nephrolepis cordifolia (L.) C. Presl, Tent. pterid.: 79 (1836), synonyms: Polypodium cordifolium L. (1753), N. tuberosa (Bory ex Willd.) C. Presl (1836), N. exaltata (L.) Schott var. tuberosa (Bory ex Willd.) Kuntze (1891).
- Nephrolepis hirsutula (Forst.) C. Presl, Tent. pterid.: 79 (1836), synonyms: Polypodium hirsutulum Forst. (1786), N. exaltata (L.) Schott var. hirsutula (Forst.) Baker (1867).
- sword ferns, ladder ferns, boston ferns (En).
- Broad sword fern, coarse sword fern (En)
- Indonesia: paku uban (Lingga), paku harupat (Sundanese), moba (southern Irian Jaya, Papua)
- Malaysia: paku larat (Malay), ch’âng yèh shèn ch’uèh (Chinese)
- Philippines: alolokdo
- Thailand: foen kaang plaa, foen teen takhaap, foen haang plaa (central)
- Vietnam: ráng thận lân.
- Common or erect sword fern, fishbone fern (En)
- Indonesia: paku acel, paku ubi (Sundanese)
- Philippines: bayabang (Tagalog), olaluent, bangduan (Igorot)
- Thailand: kut soi (northern).
- Rough sword fern (En)
- Indonesia: pakis kinca (Javanese), paku jeler, paku sepat (Sundanese)
- Philippines: alolokdo (Bisaya), bayangbang (Tagalog), lagunton (Iloko).
Origin and geographic distribution
Nephrolepis is distributed throughout the warmer parts of the world, extending into the temperate zones, but with the greatest species concentration in South-East Asia. Many species are also cultivated indoor and outdoor and, due to escapes and subsequent naturalization, natural distribution patterns are not always clear. N. biserrata is distributed pantropically and it is one of the commonest ferns in South-East Asia. N. cordifolia is distributed pantropically and sometimes also more to the north (Japan) and to the south (New Zealand). Possibly it has been introduced in East Africa and naturalized in New Zealand. N. cordifolia is only found terrestrially in open locations in the mountains of Peninsular Malaysia while in Java (Indonesia) and the Philippines it is commonly found cultivated or naturalized in the lowland. N. hirsutula is widely distributed in tropical Asia and far into the Pacific and is common in South-East Asia.
Very young curled-up leaves of N. biserrata and N. hirsutula are eaten cooked or steamed as a vegetable in Java and New Guinea. In southern Papua (Indonesia), the rhizomes of N. biserrata are dried, pounded, prepared and eaten in the same way as sago. In India and tropical America the tubers of N. cordifolia are eaten. In Java, N. biserrata is used in traditional medicine against cough. In Ivory Coast, it is applied to stop wounds bleeding. In Malaysia it is planted on a large scale as soil cover in rubber plantations because the roots release a considerable amount of nitrogen. In the Philippines a decoction of fresh leaves of N. cordifolia is used as a drink for cough, while a decoction from its tubers is applied against goitre. Young leaves of N. hirsutula are used as a poultice for swelling wounds and boils. In Papaua New Guinea Nephrolepis leaves are placed among bones in death ceremonies. In Indonesia and the Philippines the fibro-vascular bundles of the stems of N. hirsutula are extracted and occasionally used in the manufacture of hats, mats, baskets and other wickerwork. In South-East Asia and elsewhere many Nephrolepis species are used and commonly cultivated as ornamentals, including for example N. cordifolia and N. hirsutula which are popular ornamentals in Indonesia, Malaysia, Singapore, Thailand and the Philippines (both as plants and as cut leaves in flower arrangements). When grown in hanging baskets they produce hundreds of gracefully hanging, thin stolons.
Production and international trade
The genus Nephrolepis comprises some of the most popular ornamental ferns, including the 3 major species mentioned here although they are not the highest ranking. In many countries Nephrolepis species and cultivars are cultivated on a large scale and a considerable amount of international trade exists (e.g. for tropical American N. exaltata (L.) Schott cultivars). Cultivated and wild Nephrolepis species in South-East Asia are offered for sale as ornamentals on local markets only but statistics are not available.
The thin epicuticular wax layer of N. biserrata contains three drimane-type sesquiterpenes which all have a hemiacetal esterified with acetic acid. The plant contains about 7% tannin and 0.1 % essential oil and the leaves contain sequoyitol. A small amount of sugar (a hexose) is stored in the stolon buds of N. hirsutula . In the Philippines, histochemical tests indicated an abundance of alkaloids in the 3 species treated here.
Terrestrial, epilithic or epiphytic ferns with short, erect, peltately-scaly rhizomes each bearing a cluster of leaves and often also forming slender horizontal runner rhizomes or stolons with adventitious buds and sometimes tubers. Leaves pinnate, petiolate; petiole not articulated, often persistently hairy, erect to pendent; lamina long and narrow, simply pinnate with numerous and often close pinnae but the apex only pinnatifid and of indeterminate growth; rachis slightly grooved above; pinnae sessile, articulate at base, inserted on the ridges bordering the rachis groove, base often auriculate, midrib prominent and grooved, margin entire, crenate or lobed, basal pinnae often reduced, veins free, arranged in small groups for each crenation, ending in a hydathode with a white scale, fertile pinnae occasionally more incised and narrower. Sori terminal on the veins, one in each vein group, usually close to the margin, usually with circular or kidney-shaped, subpeltate, persistent indusia. Spores monolete, ellipsoid or rarely spheroidal, 25-34 μm in diameter, translucent brown, with irregularly roughened surface.
- N. biserrata . A terrestrial or epiphytic fern up to 3 m or taller. Rhizome up to 25 cm long, scales lanceolate, 3-10 mm × 0.6-0.8 mm, base peltate, margins denticulate-ciliate, apex attenuate aristate, very pale green when young, dark brown with pale brown edges when old, lustrous; stolons numerous, rather stout, in a close tuft with the leaves. Leaves tufted; petiole 12-60(-75) cm long, with linear-filiform scales shorter than those of the rhizome; lamina linear-oblong-lanceolate in outline, 1.5-2(-3.25) m × 15-30(-50) cm, pendent, chartaceous, surfaces bearing scattered small scales when young, the scales on the upper surface bearing irregularly curved hairs; rachis with up to 70 pairs of spreading pinnae, the basal ones gradually shorter and more widely spaced, the middle ones 3 cm apart, the upper ones so closely spaced as to touch each other, in large leaves often separated as wide as their width or more; sterile pinnae linear-oblong, 7-25 cm × 12-29 mm, the basal ones sometimes slightly auriculate, margins crenate, midrib hardly falcate, apex shortly acuminate; fertile pinnae 1-1.5 cm wide near the base; veins indistinct in living plants and not raised, usually once or twice forked, ending in inconspicuous hydathodes that often bear white excretions on the upper surface. Sori round, 1.5 mm in diameter, situated nearer to margin than to midrib, indusium reniform, entire, about 0.5 mm long, opening outwardly. Spores ellipsoid, monolete, low tuberculate.
- N. cordifolia . Rhizome erect, about 10 cm long, crowded with erect to arching leaves; runners numerous, up to 2 m long, often bearing scaly tubers. Petiole 5-25 cm long, scaly, deeply grooved on the upper surface; lamina in outline linear-elliptical, 30-80 cm × 4-7 cm, pinnae sessile, 40-100 on each side of the rachis, imbricating at their widened bases; sterile pinnae narrowly deltate-oblong, about 2 cm × 5-9 mm with auricled upper base, margin crenate, apex rounded or bluntly pointed, veins simple or once forked, often with lime-dotted hydathodes on upper surface; fertile pinnae at base more abruptly narrowed, in the middle about 3-5 mm wide. Sori about midway between midrib and margin; indusium 1-1.4 mm wide, attached by a broad curved base oblique to the vein, the free edge facing the apex of the pinna. Spores spheroid, tuberculate with partly fused tubercles.
- N. hirsutula . Rhizome erect, very short, bearing a tuft of leaves and many long slender runners, bearing appressed, imbricating, hairy scales 3-4 mm long. Petiole 25 cm or longer, scaly; lamina erect or arching, in outline 60-100 cm × 16 cm, pinnae very close and overlapping with their widened bases, covered with small hair-like scales when young, lowest pinnae more widely spaced and 1.5 cm long; sterile pinnae up to about 8 cm × 1.5 cm with a triangular auricle at base, margins irregularly crenate, slightly falcate at apex, veins hardly visible in living plant, ending in small hydathodes near the margin often with white scales; fertile pinnae narrower, up to about 1 cm wide. Sori close to or touching the margin; indusia round-reniform, about 1 mm in diameter.
Growth and development
The gametophyte of Nephrolepis is cordate, often bearing several-celled hairs and short-stalked antheridia. The stolons of N. biserrata can grow fast, under controlled conditions 2-4 mm per day. The apical cells are mitotically more active than the lateral ones in the organization and shaping of the stolon meristem. In tropical gardens it is often considered a weed due to its rapidly spreading runners. When kept too dry in cultivation, some species shed their pinnae quite quickly, leaving only bare dry rachises; however, when conditions improve, a new flush of leaves will develop quickly. The rachis of the leaves shows a kind of perennial growth which accounts for the crozier-like apex of many leaves. These often produce a few new pinnae long after the older pinnae have shed their spores or fallen off.
Other botanical information
Nephrolepis is often included in the Oleandraceae , or, with an increasingly wide family concept, in the Davalliaceae and Dennstaedtiaceae , respectively. Spore characters however, as well as other uncommon features such as the many stolons, the hydathodes excreting calcareous deposits, and the peltate indusium justify a separate, monotypic family. Nephrolepis is closely associated with Arthropteris J. Smith ( Oleandraceae ), which may be very similar in appearance but has long, slender, creeping rhizomes with petioles jointed to it some distance above their bases (known from Borneo and Sumatra). Nephrolepis comprises about 30 species, all closely related, many of wide distribution, about 8 in Malesia.
N. biserrata has been described under at least 16 different names and many more combinations. As a popular ornamental, N. biserrata has several cultivars, many with bizarre, dissected pinnae, of which "Furcans", with bifurcated pinnae, is best known. In the tropical New World, specimens of N. multiflora (Roxb.) Jarrett ex Morton have often been misidentified as N. biserrata .
The name N. cordifolia is under discussion because of doubts about the identity of the depicted fern of the type material which is a plate of Petiver and Plumier, by some identified as N. auriculata (L.) Trimen. N. cordifolia has relatively few cultivars. In tropical gardens, cultivar Duffii (particularly popular in the Philippines) is best known and most distinctive, forming characteristic scaly tubers used for food and water storage; its leaves are usually forked at the apices, the pinnae are subcircular and attached in more than one plane; they usually remain sterile; in cultivar Plumosa the pinnae have lobed margins. In older literature the name N. duffii Moore is used for cultivar Duffii. Mr Duff (hence the name) first discovered this form on the Duke of York's Island in New Britain, Papua New Guinea. In cooler climates the pinnae are usually longer than in the tropics.
N. hirsutula appears to be very closely related to N. acuminata (Willd.) C. Presl, which occurs in similar habitats but is more commonly epiphytic. It differs from N. biserrata in the position of the sori on small, rounded marginal lobes. However, some specimens are difficult to place in one group or the other with certainty; hybridity or other species might be involved.
N. hirsutula has been confused with N. exaltata (L.) Schott and N. biserrata , which is larger, with pinnae less close and hardly auricled at base, sori not close to the margin and usually growing in the lowland; it is not sure whether it occurs in tropical America.
The most commonly grown and horticulturally most remarkable Nephrolepis worldwide is N. exaltata (L.) Schott var. bostoniensis hort. (Boston fern, lace-fern), which has finely dissected leaves that are much shorter than in the South-East Asian species and of which numerous cultivars have been derived, including cultivars with bi-, tri- or quadripinnate leaves. Most cultivars are sterile but can easily be propagated by the stolons or by the proliferous buds on their rachises.
Most Nephrolepis species grow in thickets, on rocks and in similar, somewhat open locations; some are pioneers on lava flows, but others prefer very acid, humus-rich habitats such as peat swamps or leaf bases of palms. Some species can grow terrestrially as well as epiphytically, e.g. N. biserrata and N. hirsutula are often found on trunks of palms with persistent leaf bases (e.g. oil palm) and are very common everywhere in South-East Asia. N. biserrata is a very common lowland fern occurring in wet boggy ground, grassland, thickets, village groves, plantations, secondary forest and other regrowth conditions or on forest-grassland margins, from sea-level up to 1300 m altitude. It grows in the open or in light shade, terrestrially or on tree trunks, sometimes on rocks. It also thrives in moister conditions such as swamps and in swamp or river margins, and mangrove forest. Under favourable conditions it can spread rapidly by its long runners and form dense thickets. Together with Davallia denticulata (Burm.f.) Mett. ex Kuhn it is the first fern to invade new oil-palm plantations. In a lowland rain forest in Sabah, the fern dominated the secondary vegetation in burnt plots two years after a forest fire in Borneo. N. cordifolia is a hardy fern found in South-East Asia in various situations from shade in the lowland to open locations at higher altitudes up to 3500 m. Some cultivars tolerate temperatures down to 0°C. It can grow terrestrially, epilithically or epiphytically. N. hirsutula occurs in South-East Asia in more exposed locations than N. biserrata , from sea-level up to 2000 m altitude. In cool temperate climates N. cordifolia and N. hirsutula can overwinter in a cool greenhouse while N. biserrata needs warmer greenhouse conditions.
Propagation and planting
Nephrolepis can be propagated by spores, clump division, rhizome or stolon runner plantlets, and some species also by proliferous buds and tubers. Tissue culture is used for propagation on a large commercial scale. Runner tips produce green globular bodies when quarter-strength Murashige and Skoog medium is used supplemented with 0.5 mg/l benzyladenine (BA). Green globular bodies easily regenerate plantlets when cultured on BA-free medium, and they multiply rapidly on BA medium. Multiplication rates of over 40 per month can be realized, which means that 160 000 plantlets can be obtained from one runner tip in 6 months. Growing is quite simple because most soils and composts are acceptable as long as drainage is free. N. cordifolia can be propagated by tubers which only start sprouting in total darkness.
When grown in pots, frequent watering and occasional fertilizing of Nephrolepis are necessary. As an ornamental plant, N. biserrata should be planted outdoors or indoors in such a way that it receives the morning sun. When planted in a pot it is best grown in a mixture of soil, sand and humus (1:1:2). To promote vigorous growth N fertilizer should be applied to the leaves by spraying. Watering twice a day is appropriate when the fern is placed in the open. Too much water is as harmful as too little, and plants need bright, airy locations, in greenhouses as much as 95 lux and an optimum temperature of 24°C. Many cultivars react to stress conditions (drought, low or high temperature, poor soil) by reverting to the leaf shapes of their wild form.
Diseases and pests
In general, Nephrolepis is quite disease and pest resistant. Cultivars are particularly susceptible to botrytis, fern scale, whitefly, slugs and snails. In Bangalore (India), N. biserrata is sometimes severely infected by leafspot diseases caused by Alternaria tenuissima and Bipolaris sorokiniana (synonym: Cochliobolus sativus ). A smut ( Entyloma nephrolepidis ) has been found in Java, invading the meristematic portions of plants resulting in abnormal, sterile leaves that are wider, thicker and paler. The gall mite Eriophyes pauropus infects the leaves of Nephrolepis species, inducing the fern to form outgrowths (hollow swellings) and branched hairlets.
Handling after harvest
Freshly harvested leaves of N. cordifolia (without sporangia) placed in water for 10-20 hours at 2-4°C can be stored in perforated plastic film for 14 days without adverse effects on vase life. Even after 5 weeks' storage a vase life of 7-16 days can be expected. Wrapping the leaves in wet newspaper packed in perforated cardboard box lined with polyethene sheet gives better results than packing in airtight plastic bags.
Genetic resources and breeding
Most wild Nephrolepis species are common and widely distributed, not being overcollected for vegetable, medicinal or ornamental uses and hence not in danger of genetic erosion. Germplasm collections or breeding programmes are not known to exist.
Several Nephrolepis species are cultivated on a commercial scale. It seems worthwhile investigating the possibilities for large-scale cultivation and export of promising species and cultivars in South-East Asia. There could be a niche market for young Nephrolepis leaves as a vegetable delicacy.
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Dedy Darnaedi & Titien Ngatinem Praptosuwiryo