- Protologue: Hort. Berol. 2: 110 (1833) (often misspelled Microsorium ).
- Family: Polypodiaceae
- Chromosome number: x= 36, 37;M. linguiforme, M. membranifolium, M. scolopendria: 2n= 72;M. rubidum: 2n= 74;M. punctatum: 2n= 72, 144
Major species and synonyms
- Microsorum linguiforme (Mett.) Copel., Univ. Calif. Publ. Bot. 16: 116 (1929), synonyms: Polypodium linguiforme Mett. (1866), Pleopeltis linguiforme (Mett.) Alderw. (1909), Dendroconche kingii Copel. (1931).
- Microsorum membranifolium (R. Br.) Ching, Bull. Fan Mem. Inst. Biol. 10: 239 (1941), synonyms: Polypodium nigrescens Blume (1828), Phymatodes nigrescens (Blume) J. Smith (1866), Pleopeltis nigrescens (Blume) Bedd. (1883), Microsorum nigrescens (Blume) Copel. (1938), Phymatosorus nigrescens (Blume) Pichi Serm. (1973).
- Microsorum pteropus (Blume) Copel., Univ. Calif. Publ. Bot. 16: 112 (1929), synonyms: Polypodium pteropus Blume (1828), Pleopeltis pteropus (Blume) T. Moore (1857), Colysis pteropus (Blume) Bosman (1991).
- Microsorum punctatum (L.) Copel., Univ. Calif. Publ. Bot. 16: 111 (1929),synonyms: Polypodium punctatum (L.) Swartz (1801), Pleopeltis punctata (L.) Bedd. (1876), Microsorum musifolium (Blume) Copel. (1929).
- Microsorum rubidum (J.Smith) Copel., Gen. fil.: 197 (1947), synonyms: Drynaria rubida J. Smith (1841), Phymatodes longissima (Blume) J. Smith (1857), Pleopeltis longissima (Blume) Alderw. (1909).
- Microsorum scolopendria (Burm.f. ) Copel., Univ. Calif. Publ. Bot. 16: 112 (1929), synonyms: Polypodium scolopendria Burm.f. (1768), Polypodium phymatodes L. (1771), Phymatodes scolopendria (Burm.f.) Ching (1933), Phymatosorus scolopendria (Burm.f.) Pichi Serm. (1973).
- microsoroids (En).
M. linguiforme :
- New Guinea: koiwa (Nauti), gwau-utu (Daga).
M. membranifolium :
- Indonesia: pakis tanganan (Javanese)
- Malaysia: paku chai, paku sempak (Malay)
- Thailand: kalo rawa (Malay, peninsular).
M. pteropus :
- Winged star fern (En)
- Thailand: kut hang nok kaling (peninsular).
M. punctatum :
- Fish-tail fern, crested fern (En), climbing bird's nest fern (Am)
- Indonesia: teke (Timor), wassanke (Alor), saugtikel (Manggarai, Flores)
- Malaysia: keluwah. New Guinea: baluk (Kurte Plestok), kopeh-kopek (Matapaili), vata-vata (Kulumo)
- Philippines: eawawan (Igorot, Luzon)
- Thailand: krapok sing (south-eastern), prue mai (northern, south-western), haang nok waa (peninsular).
M. rubidum :
- Indonesia: paku leyat (Sundanese)
- Thailand: kraprok bai chaek (south-eastern).
M. scolopendria :
- East Indian polypody (Am)
- Indonesia: paku ular (Malay, Jakarta), paku cacing (Sundanese)
- Malaysia: paku wangi, sakat hitam (Malay)
- Thailand: khuut chakkhep (northern), yai phaek (peninsular).
Origin and geographic distribution
Microsorum is distributed in the Old World tropics, extending to eastern Australia and New Zealand and to most tropical islands in the Pacific. In South-East Asia, 31 species are currently recognized. M. linguiforme is distributed from India (Kerala), through non-continental South-East Asia (Sumatra, Borneo, Sulawesi, Moluccas, New Guinea) to the Solomon and Fiji Islands. M. membranifolium occurs from India, Sri Lanka and China throughout South-East Asia to the Pacific (Solomon Islands, Fiji, Society Islands, Marquesas) and Australia (Queensland). M. pteropus occurs from the Himalayas, throughout South-East Asia to China, Taiwan and Japan. It is cultivated in tropical aquariums all over the world. M. punctatum is widespread all over the tropics and subtropics of the Old World, from west tropical Africa and India, throughout South-East Asia, to southern China, northern Australia and the Pacific. M. rubidum is distributed from northern India, southern China, throughout South-East Asia except New Guinea to Taiwan, Japan and the Pacific. M. scolopendria is distributed throughout the tropics of the Old World, including tropical Africa, South and South-East Asia, Australia (Northern Territory, Queensland) and most tropical islands in the Pacific.
In New Guinea, uncooked salted leaves or young boiled leaves of M. linguiforme , M. commutatum Copel. (distributed in non-continental South-East Asia) and M. punctatum are locally eaten as a vegetable. In Malaysia and Indonesia, the young leaves of M. membranifolium are eaten steamed or cooked. In Indonesia (Java), the croziers and young leaves of M. rubidum are eaten raw or cooked as a flavouring, said to taste like bitter almonds or endive. In Malaysia and Hawaii, the fragrant leaves of M. scolopendria are used to perfume clothes and to scent coconut oils. In Indonesia, chewed rhizome of the species is applied to lizard bites in Sulawesi and Bali, and in Java a compound paste containing this species is applied to the abdomen to treat difficult labour. In Indo-China it is used as a remedy for chronic diarrhoea, in the Philippines it is said to have laxative properties and to promote perspiration. The juice from the leaves of M. punctatum is used as a purgative, diuretic and to heal wounds. The leaves have been used to cure fever, after chewing they were spattered on the head of a patient. It is easily grown as an indoor ornamental and cultivars are sold (e.g. in Australia). M. pteropus is one of the most popular aquarium plants all over the world. Several Microsorum species are occasionally cultivated as ornamentals (e.g. M. rubidum in Singapore, M. punctatum (for landscaping and as indoor pot plant cut foliage), M. thailandicum T. Boonkerd & Noot. in Thailand (also exported to United States and Europe for its remarkable blue iridescent leaves) and M. scolopendria in the Philippines).
Production and international trade
All Microsorum species are mainly collected from the wild and locally used, but statistics are not available. The aquarium fern M. pteropus is widely cultivated and traded. Since it grows in heated water tanks international trade is probably limited and local production prevails. M. punctatum is cultivated on a rather small scale (e.g. in the Philippines and in Australia as an ornamental). It is said that it has a high potential as cut foliage and large-scale cultivation in the Philippines is being promoted. M. scolopendria is abundantly cultivated in Hawaii in gardens and around resorts.
Histochemical findings of M. punctatum revealed that it contains the following substances and respective level of occurrence: alkaloids in rhizome and pinna detectable to very abundant, saponin in pinna detectable, formic acid in rhizome and pinna detectable to very abundant, oxalic acid in rhizome and pinna abundant to very abundant, and fats in rhizome and pinna detectable to abundant. The tissues of M. scolopendria contain glycyrrhizin, saponin and coumarin, the latter giving fragrance to the plant.
Ferns with rhizome short or long creeping, flattened or cylindrical, 1-10 mm in diameter, usually with a dense mat of roots; scales usually narrowly ovate, light to dark brown, (pseudo)peltate or (sub)clathrate, margin entire to dentate, sometimes hyaline, apex acuminate, with an apical hair and often marginal short glandular hairs, sometimes with a central tuft of long lax multiseptate hairs. Leaves alternating in two dorsal rows, more or less distinct, contiguous or up to 8 cm apart; petiole articulated to a phyllopodium; lamina usually simple, sterile and fertile similar, obovate, ovate or lanceolate to linear, base usually narrowly angustate, margin entire, sinuate, or undulate, apex usually acute to acuminate, membranaceous to coriaceous, usually herbaceous, with few to many small glandular hairs, occasionally with a few small scales and acicular hairs; venation more or less distinct but usually visible when viewed against the light, at least the larger veins often distinctly raised on upper surface, forming a more or less regular row of up to 10, with about equally sized areoles between each pair of adjacent secondary veins, or forming one row of main areoles parallel to the primary vein and bordered by one or two marginal rows of smaller areoles; secondary veins often slightly zigzag, free included veins 0-2 times forked, ending in hydathodes, usually directed to all sides except for some recurrent and occasionally excurrent veins near the margin. Sori roundish, 3-7 mm long or in diameter, often a few sori slightly confluent, scattered over the lamina or in one to several irregular rows between midrib and margin, usually superficial; paraphyses few to many, in most species uniseriate, occasionally once branched, l-4(-8)-celled, apex glandular. Spores monolete, bilateral, up to 75(-105) μm, smooth to slightly sculptured.
- M. linguiforme. Rhizome flattened, long-creeping, with sclerified circumvascular sheaths; scales peltate, ovate to triangular, 3-10 mm × 1-2.5 mm. Leaves simple; petiole up to 12 cm × 3-5 mm; lamina subcircular to obovate, 3-70 cm × 2-17 cm, veins prominent, connecting veins forming a single row of large areoles along the midrib bordered by several smaller ones. Sori irregularly scattered on the lower surface, generally present in the midrib areoles.
- M. membranifolium . Rhizome creeping, terete, with only scattered sclerenchyma strands, not white waxy; scales pseudopeltate, circular to triangular, 4-8 mm × 2.5-3.5 mm. Leaves pinnatifid; petiole 20-100 cm × 0.3-1 cm; lamina elliptical to ovate in outline, 27-175 cm × 36-90 cm, membranaceous, blue-green with prominent dark veins shorter than those of M. rubidum ; lobes 2-20 at each side, longest ones at position 2-10 from the base, 15-50 cm × 2-4.5(-7) cm, base decurrent and connected to a long wing about 1.5 cm wide, margin undulate and crisped, apex long-acuminate. Sori more or less in one row between the midrib and the leaf margin but usually closest to the midrib.
- M. pteropus . Aquatic fern, rhizome creeping, without sclerified circumvascular sheaths, not white waxy; scales pseudopeltate, ovate to triangular, 1.5-5 mm × 0.4-1 mm. Leaves simple, entire or deeply trilobed, very dark green; petiole 1-28 cm long; lamina (central lobe) narrowly elliptical, up to about 30 cm × 5 cm, lateral lobes smallest, base decurrent to a long wing, margin entire, apex acuminate, main veins prominent and distinct beneath, anastomosing veins forming a row of large areoles on both sides along the midrib irregularly bordered by several smaller ones. Sori irregularly scattered on the whole leaf under surface, generally absent from the marginal and midrib areoles. The apex of the leaves (particularly when submerged) occasionally producing new young plants.
- M. punctatum . Rhizome creeping, white waxy, without sclerified circumvascular sheaths; scales pseudopeltate, ovate to triangular, 1.5-8 mm × 0.5-3 mm. Leaves simple, subcoriaceous; petiole 0-12 cm long; lamina ovate to linear-elliptical, 10-175 cm × 1.5-15 cm, base decurrent into a wing along the petiole, margin entire to irregularly lobed, apex rounded to acuminate; connecting veins forming several equally sized areoles between two adjacent veins. Sori scattered on the whole lamina under surface but most frequent in upper half.
- M. rubidum. Rhizome long creeping, flattened, not white waxy, with sclerified sheaths but without sclerenchyma strands; scales pseudopeltate, ovate to triangular, 3-6 mm × 1-3 mm. Leaves herbaceous, bright green; petiole 15-120 cm long; lamina pinnatifid, elliptical in outline, 30-120 cm × 8-60 cm, larger than those of M. scolopendria , lobes 10-40 at each side of the midrib, longest ones in lower half, oblong, 7-40 cm × 1-3.5 cm, base running into a connecting wing up to 1 cm wide, margin entire, apex rounded to acuminate. Sori more or less in one row between the midrib and the margin, usually close to the midrib.
- M. scolopendria. Rhizome terete, white waxy, with sclerified circumvascular sheaths and scattered sclerenchyma strands, scales peltate, ovate to triangular, 2-7 mm × 0.6-1.4 mm. Leaves simple, entire or pinnatifid with 1-9 lobes at each side of the midrib, light green, herbaceous; petiole up to 55 cm long; lamina or lobes narrowly elliptical, up to 45 cm × 8 cm, margin entire, apex acuminate. Sori in 1-3 rows between the midrib and the leaf margin, deeply sunken and visible as protrusions on the upper surface.
Growth and development
A germinating spore of Microsorum first develops a usually heart-shaped prothallus, the gametophyte. In the sporophyte the Microsorum species with lobed leaves are thought to be more advanced than those with unlobed simple leaves. In the Philippines, spores of M. punctatum germinated about 6-7 weeks after sowing and sporophyte formation started after an additional 7 weeks.
Other botanical information
When Microsorum was established in 1833, it included only one species: M. punctatum . One century later, almost forgotten by most botanists, it was revived by Copeland (1929) in an influential publication, and included all polypodioid ferns with reticulate venation and round sori. In this broad sense it also comprised the genera Crypsinus C. Presl (now in Selliguea Bory), Lepisorus (J. Smith) Ching and Leptochilus Kaulf. and totalled about 200 species. At present Microsorum comprises about 60 species but the number varies according to inclusion or exclusion of several groups (genera) and more research is needed before the taxonomy of Microsorum can be stabilized. Microsorum is closely related to Leptochilus Kaulf., the only differences being the arrangement of the sori (sori usually fused to coenosori, forming an elongated line) and peltate paraphyses in the latter, and not fused round or elongated sori and lack of peltate paraphyses in the former). It is also close to Lepisorus which differs in its arrangement of sori (one single row between midrib and margin while in Microsorum the sori are arranged in several irregular rows or scattered). M. rampans (Baker) Paris from New Guinea is closely related or possibly conspecific with M. linguiforme . The venation in M. pteropus with its rows of areoles is characteristic; populations with only unlobed leaves have been classified as var. minor (Bedd.) Ching. When no rhizomes are available, M. membranifolium and M. rubidum are often difficult to distinguish. M. scolopendria and M. papuana (Baker) Parris (distributed in non-continental South-East Asia and Pacific Islands) are closely related and often confused; the former has sori in one to several rows, the latter usually in one row parallel to the midrib. In the Philippines, a popular cut leaf cultivar of M. punctatum is "Grandiceps".
Microsorum species are of a rather fine texture, found in moist shady locations, often on rocks or trees near streams in the forest. M. linguiforme is a low epiphyte, rarely epilithic or terrestrial in primary and secondary forests, in shady, moist locations, from sea-level up to 1650 m altitude. M. membranifolium is a fairly common epiphyte in moist, partially shaded sites, especially near streams, in the lowlands but also epilithic or terrestrial on dry rocks (particularly on limestone but also on granite) in mixed forest, from sea-level up to 1700 m altitude. M. pteropus grows terrestrially near running water, on the banks or even submerged for part of the year, but it survives and reproduces predominantly vegetatively (sori only incidentally produced) when submerged permanently; it usually occurs at low altitudes but can be found up to 1200 m. M. punctatum is usually epiphytic on tree trunks and branches, but can also be epilithic or terrestrial in various types of forest, sometimes in savanna but also in wet locations in streambeds, most common in lowland but occurring up to 2800 m altitude. It is one of the few Microsorum species inhabiting fairly open sites and can change to the crassulacean acid metabolism (CAM) pathway to limit water loss during daytime. M. rubidum is a terrestrial fern, usually in wet locations, occurring at low altitudes but sometimes up to 1500 m. In South-East Asia M. scolopendria is a common epiphyte on old trees in open locations, on the trunks of plantation oil palms, sometimes occurring on rocks and earth banks in full sunlight, from the lowlands up to 2100 m altitude.
Propagation and planting
Propagation of Microsorum is possible by spores and by rhizome cuttings. In aquariums it is recommended that M. pteropus rhizome cuttings be planted on a piece of wood or on stones to which the growing rhizome can attach itself. In the Philippines, M. punctatum is planted in a mixture of 2 parts compost and 1 part garden soil. Rhizome cuttings should be buried not deeper than 5 cm. Spores are sown on a sterilized medium and kept in a very high relative humidity. Sporophytes are transplanted in groups when they are about 1 cm tall and again transplanted individually when they are taller than 3 cm.
If planted in gardens, Microsorum can grow in pots like orchids or on dead or living tree trunks, generally requiring partial shading. In some oil-palm plantations natural stands of Microsorum are already common and could be used to start commercial exploitation. The natural stands can be tended and given horticultural care to optimize production. In rubber plantations Microsorum can be grown on the ground. In aquariums M. pteropus requires a water temperature above 20°C; it can also grow in salty water (3-5 g sea salt per litre). In the Philippines, for cultivation of M. punctatum , 75% shade is recommended, varying from 90% for the young sporophytes to about 50% for adult plants. Watering (sprinkler irrigation) is necessary as soon as the soil cover is dry, but waterlogging should be prevented. The optimum average temperature depends on the desired type of plant; at 18-20°C the fern grows slower but becomes sturdier. Monthly NPK application (14-14-14, one tablespoon per 4 litres water) is recommended.
Diseases and pests
Natural stands of Microsorum do not show signs of any serious diseases or pests. Some damage may be caused by insects and leaf deformations may occur due to fungi and viruses. M. pteropus is reported to suffer from a disease that frizzes the leaves. In the Philippines, cultivated M. punctatum is susceptible to leaf blight or leaf spot caused by Sclerotium sp. Control is difficult and infected plants can best be burned. Major pests are white louse scales ( Unaspis sp.), midrib borers, snails and slugs.
In general, when grown from spores, 2-3-year-old plants of Microsorum can be harvested as a vegetable or for other use. When grown from runners, harvesting may start 6 months after planting. In the Philippines, leaves from mature cultivated M. punctatum plants are cut when fully expanded, just before the appearance of sori. After harvest they are stored in water in the shade.
Genetic resources and breeding
Microsorum is widely distributed and common in natural stands but some species are less common. Further research is required to determine its genetic diversity. This may lead to the development of plants producing many young leaves (for vegetable use) or plants with a high coumarin content for use as a perfume. Subsequent selection and breeding programmes might result in higher-yielding cultivars.
As Microsorum can easily be grown in the shade of plantation trees there is a potential for increasing the production of young leaves for vegetable use and for coumarin production for the perfume industry. Growing Microsorum in existing plantations may reduce pressure on land utilization and at the same time increase productivity and diversification of existing plantations and products.
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H.C. Ong, Isa B. Ipor, Norma O. Aguilar & W. Somprasong