Ceratopteris thalictroides (PROSEA)
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Introduction |
Ceratopteris thalictroides (L.) Brongn.
- Protologue: Bull. Sci. Soc. Philom. Paris, sér. 3, 8: 186 (1821).
- Family: Pteridaceae
- Chromosome number: 2n= 154, 156 (tetraploid, two reproductively isolated cytotypes)
Synonyms
- Acrostichum thalictroides L. (1753),
- A. siliquosum L. (1753),
- Ceratopteris siliquosa (L.) Copel. (1935).
Vernacular names
- Floating stag's horn, pod fern, oriental water fern (En). Water sprite (Am)
- Indonesia: paku tespong, paku cai, pakis rawa
- Malaysia: paku ruan, paku roman, sayur kodok
- Philippines: makahirak-hirak, pakong sungai, pakong tubig
- Laos: kok karn pu
- Thailand: phak khaakhiat, phak kuutnam, phak kuut kao kwuang
- Vietnam: ráng gạc nai, quyết gạc nai, rau cần trôi.
Origin and geographic distribution
C. thalictroides is distributed worldwide in the tropics and subtropics, including South-East Asia. Because of its aquatic or semi-aquatic ecological requirements, in South-East Asia it is often a common weed in irrigated rice fields.
Uses
In South-East Asia especially the young leaves of C. thalictroides , before they have uncurled, make excellent greens and when cooked can be eaten as a salad or as a substitute for asparagus as a vegetable. In the Philippines this is the only fern ever grown as a food crop. In Thailand, young leaves are often blanched first. Plants can be used as a green manure in rice fields. Medicinally, this fern is used in Malaysia and the Philippines as a poultice against skin complaints, in China as a styptic to stop bleeding. Ceratopteris species, including C. thalictroides , are commercially used as ornamentals in aquaria and as model plants in all kinds of plant-based research. It is extremely useful for research because it has independent haploid and diploid life phases (thus combining features of higher and lower plant systems), a short life cycle, a simple genetic system and reproduction by single-celled haploid spores allows for the screening of extremely large numbers of individuals in a small space.
Production and international trade
For use as a green vegetable or as a medicine, production and trade of C. thalictroides in South-East Asia is limited to local markets. Worldwide it is much sold in fish hobbyist stores as a popular, easy-to-grow aquarium plant, popularly called "water sprite".
Properties
Per 100 g edible portion, young fern leaves of C. thalictroides contain approximately 230 mg protein, 150 mg P2O5, 150 mg CaO, 120 mg Fe and 300 mg Mg. Alkaloids, arbutin and tannin have been found in the green parts.
Description
- A highly polymorphic, unbranched, light green, aquatic or semi-aquatic fern, usually rooted in soil, up to 1 m tall.
- Rhizome short, erect, sparsely scaly, bearing a rosette-like tuft of leaves; scales broadly ovate, 2 mm × 1.5 mm, base truncate or cordate, entire, apex acute terminating in a thin, glandular, translucent cell with dark lateral cell walls; roots borne on the petiole at or near the base.
- Leaves dimorphous, succulent; petiole thick, fleshy, sometimes inflated, filled with large air-cells, up to 50 cm long and 1 cm in diameter at base, rounded and ribbed on the underside, flattened and smooth above, sparsely scaly with broad, flaccid, appressed, often circular or reniform, light brown scales; rachis and other axes of the leaf herbaceous with tissue virtually undifferentiated and continuous from the axes onto all the various segments; sterile laminas 1-3-pinnate, subdeltate to ovate or oblong, 2-40 cm × 2-20 cm, usually shorter and wider than in fertile leaves, glabrous, often provided with proliferous buds in the axils of pinnae or sinuses of segments; sterile segments lobed or incised, up to about 12 cm long, ultimate lobes linear, acute; fertile laminas larger, more erect and more copiously divided, 3-4-pinnate, up to 100 cm × 50 cm, pinnules divided into linear acute lobes up to 5 cm × 2 mm, the margin revolute and covering the sporangia; mature leaves turn brown and will expose the sporangia which then start releasing spores.
- Sporangia scattered individually along the veins on the lower lamina surface, short-stalked (appearing sessile), large, the annulus longitudinal, irregular, composed of 20-71 slightly indurated cells, sometimes interrupted at the apex as well as at the stalk.
- Spores 32 per sporangium, tetrahedral, 96-124 μm in diameter, pale yellow, translucent, with raised superficial lines forming a network of irregular long meshes.
Growth and development
The buds present in the axils of the pinnules of C. thalictroides can serve as a means of vegetative propagation which is supposed to be the principal mode of reproduction. The depth of water in which spores will germinate is unknown. Old plants are always more or less submerged in water at their bases, where they also can bear roots. The length of the stipes is probably determined by the depth of the water. Young plants mainly produce sterile leaves; on well-grown mature plants leaves are usually fertile. C. thalictroides has a short, upright rhizome and often grows as an annual. In non-seasonal waters, however, it may live for several years and attain a considerable size. In vitro, a spore germinates in 3 days on a simple inorganic nutrient medium and a mature gametophyte develops within 6 days of germination. The gametophyte consists of a small (less than 2 mm), simple, two dimensional thallus with rhizoids, vegetative cells and sexual organs (antheridia and archegonia). Sexual differentiation is controlled by a pheromone. In the presence of water the antheridia release sperms which swim to the archegonia to fertilize eggs. After fertilization the zygote starts to grow, becoming a 5-20 cm tall sporophyte with a short upright rhizome, roots and leaves. When mature, spore production is continuous by meiosis, which occurs within the sporangia that are located on the margins of fertile leaves. Spores remain viable for many years and can be stored at room temperature. The whole cycle from spore to spore can be completed in less than 30 days. Detached juvenile leaves placed on moist soil readily produce aposporous prothalli. Older leaves produce shoot buds under these circumstances.
Other botanical information
The genus Ceratopteris Brongn. comprises an ancient group of ferns which has been variously classified, mainly because its evolutionary relation to other genera or groups is not clear as a result of extinction. Here it is classified in the subfamily Ceratopteridoideae of the family Pteridaceae. In the literature it has been classified in, for example, Adiantaceae, Parkeriaceae, or in the so-called Adiantum-group. Ceratopteris comprises 3-4 species, all edible, most of them diploid (2 n = 78) but C. thalictroides is tetraploid. C. pteridoides (Hook.) Hieron. is principally limited to Central and South America, but in South-East Asia it also occurs in Vietnam. It is easily recognized by its simple sterile leaves. C. cornuta (Beauv.) Le Prieur is mainly confined to tropical Africa and is nowhere common; it much resembles C. thalictroides and in the past the two were often considered identical. C. richardii Brongn. occurs in tropical America and Africa, but it much resembles C. thalictroides and it is questionable whether it is a different species (diploid, 16-spored sporangia, against tetraploid and 32-spored sporangia in C. thalictroides).
Ecology
In South-East Asia, C. thalictroides is commonly found in swamps, shallow water rice fields, along ditches and ponds with the greater part of its leaves exposed to air, throughout the lowlands in sunny locations. Its life cycle makes the plant well adapted to seasonal fluctuations in the water level.
Propagation and planting
Propagation of C. thalictroides is by spores, by rhizome cuttings and by a kind of bulbil (bud) present in the axils of pinnules. Spores can float on water; they will germinate readily and produce young plants both submerged in water and on the surface of wet mud exposed to air. Submerged plants develop most quickly.
Husbandry
C. thalictroides is sometimes cultivated for food but not commercially. Farmers harvest the plants from rice fields and swampy locations for local consumption. In the Philippines it was once cultivated in a paddy field on a larger scale, but was destroyed by a fungus.
Diseases and pests
In the Philippines plants of C. thalictroides were completely destroyed by an unidentified fungus.
Harvesting
Young leaves of C. thalictroides are collected for cooking while mature plants are used for green manure.
Genetic resources and breeding
C. thalictroides is distributed pantropically and is not in danger of extinction. Germplasm collections or breeding programmes are not known to exist, also because in agriculture it is considered a weed. Its value as a model plant for plant breeding research is considerable.
Prospects
In most areas the use of C. thalictroides as a vegetable or as a green manure is also a method of weed control in rice fields. With increasing use of herbicides its weedy occurrence will decrease and possibly also its consumption. In South-East Asia it will remain a fern of minor importance. Its use as an aquarium ornamental and as a model plant in research will guarantee a continuing interest.
Literature
- Amoroso, V.B., 1990. Ten edible economic ferns of Mindanao. The Philippine Journal of Science 119(4): 295-313.
- Devol, C.E. & Shieh, W.-C., 1994. Parkeriaceae, Ceratopteris. In: Huang, T.-C. (General Editor): Flora of Taiwan. 2nd Edition. Vol. 1. Pteridophyta and Gymnospermae. Editorial Committee of the Flora of Taiwan, Taipei, Taiwan. pp. 535-536.
- Holttum, R.E., 1966. A revised flora of Malaya. 2nd Edition. Vol. 2. Ferns of Malaya. Government Printing Office, Singapore. pp. 577-579, 638.
- Lloyd, R.M., 1993. Parkeriaceae. In: Flora of North America. Vol. 2. Pteridophytes and Gymnosperms. Oxford University Press, New York, Unites States. pp. 119-121.
- Tagawa, M. & Iwatsuki, K., 1985. Ceratopteris. In: Tagawa, M. & Iwatsuki, K. (Volume editors), 1979-1989. Pteridophytes. In: Smitinand, T., Larsen, K. (Series editors): Flora of Thailand. Vol. 3. Forest Herbarium, Royal Forest Department, Bangkok, Thailand. pp. 183-185.
Authors
Chanpen Prakongvongs
