Ophioglossum reticulatum (PROSEA)
- Protologue: Sp. pl.: 1063 (1753).
- Family: Ophioglossaceae
- Chromosome number: n= 120, 240, 360, 480, 510, 630 + 10 fragments, 720; the latter counts, corresponding with chromosome numbers of 1260-1440 in the sporophyte, are the highest found in any living organism; various cytotypes have been found coexisting in a single population
Ophioglossum petiolatum Hooker (1823), O. moluccanum Schltdl. (1825), O. pedunculosum sensu auct. plur., non Desv.
- Adder's-tongue fern (En)
- Indonesia: jukut siraru (Sundanese), daun saleh (Moluccas), jumu tufa (Ternate)
- Philippines: ground-adder's tongue fern.
Origin and geographic distribution
O. reticulatum is distributed pantropically, both in the tropics and subtropics, including South-East Asia.
In Indonesia, O. reticulatum is an appreciated vegetable, collected sedulously wherever it is common. It is eaten fresh as salad, or cooked, alone or mixed with other vegetables. The leaves should be cooked gently, otherwise they turn completely into slime. In South Africa (Natal) and India the leaves are used as a substitute for spinach. In the Philippines, it is used as a herbal medicine which is anti-inflammatory and anti-swelling. Leaves boiled in oil are a remedy for wounds.
Production and international trade
O. reticulatum is collected from the wild and traded only locally; statistics are not available.
Young leaves of O. reticulatum taste sweet. The presence of alkaloids, arbutin, amygdalin, saponin, formic acid and oxalic acid in most plant parts has been shown through histochemical tests in the Philippines.
A small, terrestrial, erect, herbaceous fern with a single spike and few entire leaves. Rhizome subterranean, short cylindrical to subglobose, 10-22 mm × 2 mm , sometimes stoloniferous, resulting in the formation of colonies, carnose, glabrous, bearing rather thick roots and 1-2(-8) leaves. Leaves entire with a long-petiolate spike; petiole terete, (0-)2-16 cm long, green; sterile lamina very variable, ovate to lanceolate, reniform, deltoid or orbicular, rarely obovate or trullate, (0.8-)1-8(-10.5) cm × 0.5-5 cm, base attenuate to cordate, margin entire, apex acuminate to obtuse, green, carnose, thin or coriaceous when dry; venation obscure to conspicuously reticulate, lax with few free-ending veinlets to rather dense and with many free veinlets without or with a few areolulae. Strobilus spike-like on a 1-20 cm long stalk which arises from lamina base, (1-)5-6(-8) cm long, sterile apex 0.5-1.5 mm long; sporangia 20-45 pairs in two rows, connate and sunken into the tissue, yellow-green, opening by a transverse slit. Spores trilete, subglobose, surface finely reticulate but seemingly smooth, blackish.
Growth and development
The tuberous, fleshy, non-green prothalli of O. reticulatum grow buried in the soil and depend on a mycorrhizal fungus. The apices are whitish, the lower parts greyish, yellowish, or brownish. The prothalli are long-lived perennials of indeterminate growth and each may give rise to one or several sporophytes. The completion of the life cycle may take 1-20 years (the fastest gametophyte maturation recorded for Ophioglossum sp. in culture is 8 months). Gametophytes can develop a sporophyte when grown in an sterile culture medium with nutrients including ammonia and supplements of sugar. The antheridia and archegonia occur together in various stages of development, arising from cells on the surface, but at maturity they are largely sunken in it. The sporophytes have fleshy rhizomes and roots which can penetrate deep into the soil. In a dry season, aboveground parts may die; growth is resumed at the beginning of the rainy season.
Other botanical information
The Ophioglossaceae is the most isolated family of the ferns and some authors consider it more closely related to a lineage of progymnosperms or cycadophytes than to typical modern ferns. Evidence from fossils to back up speculations, however, is lacking. The sporophore is unique and not found in other fern families. Within the genus Ophioglossum L., O. reticulatum belongs to subgenus Ophioglossum , with 4 closely related species in South-East Asia; they are all terrestrial, there is a good demarcation between petiole and lamina, the stalk of the spike is not or only at the base adnate to the lamina and the spike has a sterile apex. The other members of subg. Ophioglossum are: O. costatum R. Br. (Old World tropics), O. gramineum Willd. (pantropical) and O. nudicaule L.f. (pantropical). The differences with O. reticulatum are small and concern mainly the size and form of the rhizome and the leaf blade. O. reticulatum is spread pantropically and is very variable. Mainly based on leaf characteristics, it has been subdivided into species, subspecies, varieties and formas, causing confusion in the literature on its identity. The presence of many intermediates makes those subdivisions rather useless and it seems better to accept one widespread polymorphic species.
O. petiolatum Hooker from South America, treated as a synonym here, is often considered as a different species. It is not sure whether what has been identified as O. petiolatum in Asia is identical to the original O. petiolatum and thus it is uncertain if it is identical to O. reticulatum .
In addition to O. pedunculosum , also O. pedunculatum has been used as a synonym. This is based on a type-error by Poiret (1816) and persistently copied since. Poiret wrote O. pedunculatum instead of O. pedunculosum and many authors have confused both names with O. reticulatum .
The closely related northern temperate O. vulgatum L. has been widely used for various medicinal purposes. In traditional European medicine, an ointment made from the leaves was used as a general treatment for wounds. The juice was a constituent of eyewashes. In Belgium O. vulgatum was applied to snake bites. In Chinese medicine O. vulgatum is turned into general tonics and reported to be emetic, antiscrofulous, and useful for dropsy, vomiting and hiccough; fresh leaves are used as a poultice for ulcers.
O. reticulatum can be found in humid, mostly shaded but also sunny sites, from sea-level up to 2200 m altitude. It often grows in a colony above the ground surface and on bare soil that is not easily water permeable because of a rocky base, a termite nest, or on a well-trodden place (for example along paths, roads and houses). Its presence may indicate poor soil. Sometimes it grows in humid grassland vegetation. The plant is usually only visible in the rainy season. In agriculture it can become a harmless weed.
Propagation and planting
O. reticulatum can be propagated by spores or rhizome cuttings. Because of its stoloniferous habit it can develop rather extensive colonies. Commercial cultivation is not practised, but for its medicinal properties it is often grown in pots. When grown from spores, 1-2-year-old plants can be harvested for their leaves; when grown from plants collected from the wild, harvesting may start after about 6 months.
Genetic resources and breeding
O. reticulatum is widespread and there seems to be no danger of extinction. The conservation status of its various cytotypes and varieties, however, is largely unknown. Collection of germplasm is recommended to safe the wide variability. Neither germplasm collections, nor breeding programmes are known to exist.
Because O. reticulatum has nutritional, medicinal and ornamental value, it seems worthwhile investigating further its properties and possibilities for cultivation and breeding.
- Campbell, D.H., 1911. The Eusporangiatae, the comparative morphology of the Ophioglossaceae and Marattiaceae. Carnegie Institution of Washington, Washington, United States. 229 pp.
- Holttum, R.E., 1966. A revised flora of Malaya. 2nd Edition. Vol. 2. Ferns of Malaya. Government Printing Office, Singapore. pp. 39-40, appendix 2.
- Khandelwal, S., 1990. Chromosome evolution in the genus Ophioglossum L. Botanical Journal of the Linnean Society 102: 205-218.
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- Zamora, P.M. & Co, L., 1986. Guide to Philippine flora and fauna. Vol. 2. Economic ferns, endemic ferns, gymnosperms. Natural Resources Management Center, Ministry of Natural Resources and University of the Philippines, Goodwill Bookstore, Manila, The Philippines. p.18.
V.B. Amoroso & H.C. Ong