Pityrogramma calomelanos (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Pityrogramma calomelanos (L.) Link

Protologue: Handbuch 3: 20 (1833).

Family: Pteridaceae

Chromosome number: 2n= 232 (tetraploid)

Synonyms

• Acrostichum calomelanos L. (1753),
• Pellaea calomelanos (L.) Link(1841).

Vernacular names

• Silver fern, silverback fern (En)
• Indonesia: pakis perak (Javanese), paku perak (Sundanese), pakis wulung (Sumatra)
• Malaysia: paku hijau (Malay), fen yèh ch’uèh (Chinese)
• Philippines: pakong-gubat (Tagalog), elecho de plata (Tagalog), pakong-kalabao (Tagalog)
• Thailand: chon nok khao (Yala), chon rung (Pattani), foen ngoen (Bangkok)
• Vietnam: cho chanh.

Origin and geographic distribution

P. calomelanos originates from tropical and subtropical America but has spread throughout the tropics, including South-East Asia. It has been cultivated for a long time and its current, almost pantropical distribution may have been induced by deliberate introductions. Its spread throughout the Old World tropics went by roads and plantations. If its current distribution is not due to man directly, then at least P. calomelanos takes advantage of the many open habitats created by human activities.

Uses

In the Philippines, a decoction of the leaves of P. calomelanos, with the roots of Cynodon dactylon (L.) Pers. and styles of Zea mays L., is considered an effective remedy for kidney trouble. A decoction of the roots of P. calomelanos is drunk to treat dysentery. To cure malaria, the leaves are pounded and rubbed on the back and placed under a sleeping mat. P. calomelanos is also used medicinally by Chinese Malaysians and is often cultivated as an ornamental in gardens and greenhouses.

Production and international trade

Although P. calomelanos is a plant cultivated worldwide no statistics on production or trade are available.

Properties

P. calomelanos produces a conspicuous white waxy resinous substance on the lower leaf surface, as do a number of other species in the Pteridaceae. The major components of this wax are flavonoids (chalcones, dihydrochalcones, flavanones, dihydroflavonols, flavones, flavonols), some of them with a complex substitution pattern, including esters, C-methyl derivatives and biflavonoids. Diterpenoids and triterpenoids are also present sometimes. The wax of P. calomelanos contains complex flavonoids such as calomelanol A (8-[3-(4-methoxyphenylpropionyl)]-5,7-dihydroxydihydroneoflavone), calomelanol B (8-[3-(4-hydroxyphenylpropionyl)]-5,7-dihydroxydihydroneoflavone), calomelanol C (8-(3-phenylpropionyl)-5,7,4'-trihydroxydihydroneoflavone), 8-(3-phenylpropionyl)-5,7-dihydroxyneoflavanone, 8-(2-carboxy-1-phenylethyl)-5,7-dihydroxyflavone δ-lactone and seven others called calomelanol D-J. The wax also contains a cytotoxic component (2'6'-dihydroxy-4'4-dimethoxy dihydrochalcone). In tests on mice injected with Ehrlich ascites cells, the life span was increased by 52% and 57% when a liposome preparation of the chalcone was administered at 5 mg/kg and 25 mg/kg, respectively. The leaves of P. calomelanos contain the sesquiterpenes pterosin Z and calomelanolactone. In the Philippines, histochemical tests on P. calomelanos revealed the presence of alkaloids, amygdalin, saponin, oxalic acid, arbutin, tannin, formic acid and tartaric acid.

Description

• A terrestrial, closely tufted, rhizomatous fern up to about 1 m tall.
• Rhizome short, ascending to erect, covered with scales; scales lanceolate, 4-5 mm long, dark golden brown, thin, entire, the apex filamentous.
• Leaves 2-4-pinnate; petiole 10-50 cm long, lustrous dark purple, with a few scales near the base, glabrous upwards, covered with white waxy powder when young; lamina lanceolate to oblong-deltate, 20-95 cm × 10-30 cm, the apex acuminate, herbaceous to coriaceous, light green and glabrous above, underside with a white (more rarely pale yellow or pink) waxy covering exuded by glandular hairs; rachis grooved on upper surface; pinnae linear-subtriangular, up to 13 cm × 1-4 cm, gradually smaller upwards, or longer near the middle, the lower ones petiolate, cuneate-truncate at base, the apex acuminate, the costa grooved, grooves decurrent to those on the rachis; pinnules oblong-lanceolate, up to 2.2 cm × 0.5 cm, cuneate at base, acute to acuminate at apex, lobed or pinnatisect in larger ones; lobes oblanceolate to spatulate, acute and dentate at apical portion; veins free, pinnate in larger ones, to several times forked, obscure.
• Sori along veins throughout the lower surface and often concealing it, exindusiate.
• Spores subtriangular, prominently ridged, 39-54 μm.

Other botanical information

Pityrogramma Link comprises about 16-20 species, with most species in tropical America. Pityrogramma is now usually classified in Pteridaceae, but in the literature it can also be found under Adiantaceae, Gymnogrammaceae, Parkeriaceae and Sinopteridaceae. P. calomelanos is very variable and, based on the type and colour of the indumentum, 3 major varieties have been distinguished but much confusion exists:

• var. austroamericana (Domin) Farwell. Characterized by a cover of glandular hairs exuding a yellow farinose wax at underside of leaves. Mainly occurring from Costa Rica to Brazil, but occasionally also in tropical Asia. Contrary to var. calomelanos, this variety is more widely distributed in the subtropics and warm-temperate regions than in the humid tropics. Some authors consider this taxon as a separate species: P. austroamericana Domin (synonyms: P. calomelanos var. austroamericana (Domin) Farwell, P. calomelanos var. aureo-flava auct. non (Hook.) Weatherby ex Bailey, P. chrysophylla auct. non (Sw.) Link). It is a popular ornamental, known as golden fern or gold-dust fern, with bright yellow to orange powder on the leaf underside.

• var. calomelanos. Characterized by a cover of glandular hairs exuding a white farinose wax on underside of leaves. Occurring naturally in tropical America. Elsewhere often cultivated in greenhouses and gardens and often escaped and naturalized, for example in Africa and tropical Asia. In tropical South-East Asia, var. calomelanos is the most common form and this paper mainly refers to this variety.

• var. ochracea (C. Presl) R.M. Tryon. Characterized by scattered trichomes instead of glandular hairs at underside of leaves. Occurring from Honduras to Bolivia, and not in South-East Asia. Some authors consider this taxon as a separate species: P. ochracea (C. Presl) Domin.

The subdivision of P. calomelanos into varieties is difficult because the characteristics are not constant and escapes from cultivation and possibly hybridization occur.

P. chrysophylla (Sw.) Link (synonym: P. calomelanos var. aureo-flava (Hook.) Weatherby ex Bailey), originating from the West Indies, is another popular ornamental pot plant in South-East Asia with a golden powdery covering on the underside of the leaves and is also named golden fern.

Ecology

P. calomelanos occurs on open mountain slopes in recently felled areas or along new roads at low or medium altitudes, in open forest, savanna woodland and rainforest margins. It is distinctly tropical, apparently preferring non-calcareous fine sands. After volcanic eruptions it may be one of the first or even the most important species recolonizing the area, both from spores and from remaining rhizomes.

Propagation and planting

P. calomelanos can be propagated by spores and by rhizome cuttings.

Husbandry

P. calomelanos prefers slightly drier conditions than most ferns and the plants are easy to grow. It requires a well-drained potting mix and should be exposed to moderate sunshine.

Genetic resources and breeding

P. calomelanos is widespread and common, and not in danger of genetic erosion. Germplasm collections or breeding programmes are not known to exist.

Prospects

P. calomelanos contains many specific chemical constituents, especially in the waxy exudates. Little is known about the medicinal and other properties of these substances and research is recommended. Similar to Pteris vittata L. (see the treatment on Pteris L.) it is tolerant of high concentrations of heavy metals and it hyperaccumulates arsenic. However, phytoremediation of arsenic contaminated soils with the aid of ferns is a very recent development in which Pityrogramma has so far received much less attention than Pteris, although it is called equally promising. Its ornamental value will remain important and further research is needed into the possibilities for commercial production in South-East Asia.

Literature

• Asai, F., Iinuma, M., Tanaka, T., Takenaka, M. & Mizuno, M., 1992. Five complex flavonoids in the farinose exudate of Pityrogramma calomelanos. Phytochemistry 31(7): 2487-2490.
• Bostock, P.D., 1998. Pityrogramma. In: McCarthy, P.M. (Editor): Flora of Australia. Vol. 48. ABRS/CSIRO, Melbourne, Australia. pp. 263-264.
• Joe, B., 1958. Ferns cultivated in California: Woodwardia, Aglaomorpha, Pityrogramma. Lasca Leaves 8(3): 60-65.
• Panigrahi, G., 1975. The genus Pityrogramma (Hemionitidaceae) in Asia. Kew Bulletin 30: 657-667.
• Schelpe, E.A.C.L.E., 1975. Observations on the spread of the American fern Pityrogramma calomelanos. British Fern Gazette 11: 101-103.
• Sukumaran, K. Ramadasan, K. & Kuttan, R., 1991. Screening of 11 ferns for cytotoxic and antitumor potential with special reference to Pityrogramma calomelanos. Journal of Ethnopharmacology 34(1): 93-96.
• Tryon, R., 1962. Taxonomic fern notes. 2. Pityrogramma (including Trismeria) and Anogramma. Contributions from the Gray Herbarium of Harvard University 189: 52-76.
• Visoottiviseth, P., Francesconi, K. & Sridokchan, W., 2002. The potential of Thai indigenous plant species for the phytoremediation of arsenic contaminated land. Environmental Pollution 118: 453-461.
• Wollenweber, E. & Schneider, H., 2000. Lipophilic exudates of Pteridaceae - chemistry and chemotaxonomy. Biochemical Systematics and Ecology 28(8): 751-777.

Authors

Dedy Darnaedi & Titien Ngatinem Praptosuwiryo