Portulaca (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Portulaca L.

Protologue: Sp. pl.: 445 (1753); Gen. pl., ed. 5: 204 (1754).

Family: Portulacaceae

Chromosome number: x= unknown. P. oleracea: 2n= 18, 36, 45, 54 (a polyploid complex); P. quadrifida: 2n= 48

Major species and synonyms

• Portulaca oleracea L., Sp. pl.: 445 (1753), synonyms: P. oleracea L. ssp. oleracea , P. oleracea L. ssp. sativa (Haw.) Schübl. & Mart. (1834).

• Portulaca quadrifida L., Mant. pl. 1: 73 (1767).

Vernacular names

Portulaca oleracea:

• Purslane (En)
• Pourpier (Fr)
• Indonesia: gelang, krokot (Java), re-sereyan (Madura)
• Malaysia: gelang pasir, segan jantan, rumput beremi
• Philippines: golasiman (Tagalog), ngaluk (Ilocano), alusiman (Bicol)
• Cambodia: maông dâb phkaa
• Laos: taa kôngz, biaz
• Thailand: phakbia-yai (central), phakbia-dokluang
• Vietnam: rau sam.

P. quadrifida:

• Single-flowered purslane (En)
• Indonesia: kremi, gelang pasir
• Malaysia: rumput segan
• Philippines: sayikan (Tagalog), marangalog (Ilocano)
• Thailand: phakbia-nu (central), phakbia-lek.

Origin and geographic distribution

Portulaca is a genus of about 40 species, mainly tropical and subtropical in distribution. In South-East Asia 5 species occur. P. oleracea is a cosmopolitan weed (wild and cultivated) whose origin is unknown. Mexico and Australia are considered to be centres of diversity. The cultivated forms probably originated in the Old World. P. quadrifida is a pantropical weed (wild and rarely cultivated) whose origin is also uncertain. It does not occur in Australia or in the Pacific east of Samoa.

Uses

Purslanes are believed to be among the earliest vegetables of mankind. The leaves and young shoots can be eaten raw. They have a mild pleasant flavour and are frequently used in salads. They can also be cooked and consumed as a spinach dish. It is a good feed for pigs, chickens, and birds like canaries. Large forms are sometimes planted as ornamentals.

P. oleracea is included in the World Health Organization's list of most used medicinal plants. The general uses are as diuretic, to treat rheumatism and gynaecological diseases, as a sedative, analgetic and cardiotonic, to treat fever, disorders of the urinary tract, worm diseases, as tonic and choleretic, to treat dysentery, and to apply externally to ulcers, eczema and dermatitis. Experimentally it has been shown to have no anti-cancer activity, but to have a definite anti-viral, anti-bacterial, anti-fungal action, to be a sedative, and to lower levels of glucose in the blood. P. quadrifida is used less widely but has similar medicinal applications.

Production and international trade

Most purslane in South-East Asia is gathered from naturally occurring stands. Some P. oleracea is produced commercially in European countries. No production or trade statistics are available.

Properties

Per 100 g edible portion, P. oleracea contains: water 92 g, protein 1.7 g, fat 0.4 g, carbohydrates 3.8 g, Ca 103 mg, P 39 mg, Fe 3.6 mg, vitamin A 2550 IU, vitamin B₁ 0.03 mg, and vitamin C 25 mg. The energy value is 88 kJ/100 g.

Both species may contain oxalates in toxic quantities, which may cause death in livestock. In some soils they also tend to accumulate nitrates and thus should be consumed in moderate quantities.

The entire plant of P. oleracea contains the alkaloid norepinephrine. The red pigments are acylated betacyanins. The 1000-seed weight is 0.4-0.5 g.

Description

• Mostly succulent, copiously branched herbs.
• Leaves opposite or spirally arranged, linear to orbicular, in most species with axillary hairs.
• Flowers in (1-)2-30-flowered, terminal capitula; receptacle funnel-shaped, mostly with hairs or scales in the axils of the bracts, surrounded by a whorl of 3-30 involucral leaves; sepals 2, occasionally keeled or hooded, persistent or caducous with the petals, stamens and style; petals 4-6(-8), usually obovate, occasionally emarginate or mucronate; stamens 4 to numerous, arranged in 1 whorl; ovary half-inferior, style with 2-18 arms.
• Fruit a capsule with a deciduous circumscissile operculum.
• Seeds numerous.

P. oleracea:

• Erect or ascending annual herb, up to 50 cm tall.
• Leaves obovate to spathulate, 2-40 mm × 1-20 mm, axillary hairs inconspicuous, up to 1 mm long.
• Capitula 2-30-flowered, involucral leaves 2-8, sepals carinate, up to 6 mm × 6 mm; petals (4-)5, broadly obovate, up to 7 mm × 6 mm, yellow; stamens 7-10(-15); style usually with 5 arms.
• Fruit ovoid, ca. 4 mm × 3 mm.
• Seeds 0.5-1.2 mm in diameter, granulate; testa cells stellulate with many fine tubercles.

P. quadrifida:

• Creeping herb, rooting at the nodes; nodes with a whorl of hairs.
• Leaves all opposite, elliptical to cordate, 2-20 mm × 1-7 mm, axillary hairs 5 mm long.
• Capitula 1(-3)-flowered, involucral leaves 4; sepals ca. 3 mm long; petals 4, obovate, up to 5 mm × 4 mm, yellow; stamens 8 or 12; style usually with 4 arms.
• Fruit obovoid, 2-3.5 mm long.
• Seeds 0.8-1 mm in diameter; testa cells elliptical, radially arranged, surface convex or with a tubercle.

Growth and development

P. oleracea completes its life cycle in the tropics in 2-4 months. Early growth is slow but accelerates after 2 weeks. It flowers early and year-round. Self-pollination in the bud is the rule. Capsules ripen in 7-12 days from flowering. Purslanes are not considered very harmful weeds because of shallow rooting; nevertheless, P. oleracea is often listed as one of the world's worst weeds. They are easily dispersed by running water. Seeds are easily spread by wind, water, with crop seeds or through bird droppings.

Other botanical information

P. oleracea is a very variable species, the variability also being expressed by the existence of diploid, tetraploid and hexaploid populations. Up to ten subspecies have been distinguished, mainly based on seed size and seed-coat cell morphology, but a convincing classification, including all existing populations of the world, is still lacking. For a long time the species has been subdivided into two subspecies or varieties: ssp. oleracea (synonyms: var. sylvestris (Mont.) DC., ssp. sylvestris (Mont.) Celak) for the wild diploid or tetraploid forms; and ssp. sativa (synonym: var. sativa (Haw.) DC.) for the cultivated forms, being hexaploid with 2n= 54. The cultivated forms, which usually have taller plants and larger seeds, can best be distinguished botanically at cultivar level. The existence of numerous intermediate forms raises doubts about the value of classification into subspecies.

P. quadrifida is often confused with P. pilosa L. (rose-flowered purslane), also a very variable pantropical weed, sometimes used as ornamental plant. P. pilosa has spirally arranged leaves, obovate to linear, up to 30 mm × 4 mm; petals 4-6, pink, red to yellow, stamens 10-75, style arms 4-8.

Ecology

Both species are common weeds throughout the warmer parts of the world. Because P. oleracea is more tolerant of lower temperatures, it occurs in Java up to elevations of 1800 m, whereas P. quadrifida is restricted to the lowlands. They are often involuntarily introduced by the agency of man and readily occupy newly disturbed areas and cultivated fields. Like Amaranthus L., the genus Portulaca is characterized by the C4-cycle photosynthetic pathway, which means a high photosynthesis at high light intensity and temperatures. Fresh seeds need light for germination, but this requirement disappears in older seeds. Generative development seems not to be influenced by photoperiod. The purslanes are tolerant of a wide range of soils but they prefer sand or sandy loams. In P. oleracea , populations are often adapted to certain climatic and edaphic conditions. Diploid populations often grow as halophytes in coastal areas, tetraploids are found in the widest range of latitudes and altitudes, and hexaploids are found mainly at high latitudes and altitudes.

Agronomy

Under natural conditions, purslanes generally perpetuate by reseeding, but stem fragments also easily re-root after being cut. In cultivation, propagation is also by seed. Seeds are very small, and they are usually mixed with sand before being broadcast or direct-seeded in rows. Because purslane is shallowly rooted and a crop of short duration, the topsoil should be of good fertility. There is little information on diseases and pests. Damping-off of young seedlings is a common problem.

When cultivated commercially, purslanes can be harvested by uprooting or by 2-3 successive cuts. The first cut is 3-4 weeks after sowing, and subsequently at intervals of 2 weeks. After 1½-2 months, flowering interferes with quality.

Top yields in Europe are about 50 t/ha per crop or 2-2.5 kg/m² per cutting round. In the tropics yields of 12-17 t/ha have been reported.

Purslane can be stored for 3-5 days at 0-1 °C and high relative humidity.

Genetic resources and breeding

The wide distribution of the Portulaca species points to great genetic flexibility that rapidly permits adaption to new environments. Large variation is available in natural populations, but no germplasm collections exist. Some improved cultivars with larger leaves have been selected for vegetable use. Green- and yellow-leaved types are listed in European seed catalogues.

Prospects

P. oleracea is decreasing in importance in temperate areas, but it might become a rather popular vegetable in tropical areas. More information on the extent of the utilization of purslanes in various parts of South-East Asia would be useful. There is a need for higher yielding cultivars with good market quality.

Literature

• Danin, A., Baker, I. & Baker H.G., 1978. Cytogeography and taxonomy of the Portulaca oleracea L. polyploid complex. Israel Journal of Botany 27: 177-211.
• Dharma, A.P., 1987. Indonesian medicinal plants. Balai Pustaka, Jakarta, Indonesia. pp. 81-82.
• Fritz, D., Stolz, W., Venter, F., Weichmann, J. & Wonneberger, C., 1989. Gemüsebau [Vegetable growing]. 9th revised edition. Ulmer, Stuttgart, Germany. pp. 316-317.
• Geesink, R., 1971. Portulacaceae. In: van Steenis, C.G.G.J. et al. (Editors), 1950- . Flora Malesiana. Series 1. Vol. 7. Noordhoff International Publishing, Leyden, the Netherlands. pp. 121-133.
• Holm, L.G., Plucknett, D.L., Pancho, J.V. & Herberger, J.P., 1977. The world's worst weeds: distribution and biology. East West Centre, University Press, Hawaii, United States. pp. 78-83.
• Soerjani, M., Kostermans, A.J.G.H. & Tjitrosoepomo, G., 1987. Weeds of rice in Indonesia. Balai Pustaka, Jakarta, Indonesia. pp. 490-491.

Authors

• S. Susiarti