Polyalthia (PROSEA Medicinal plants)
Introduction |
Polyalthia Blume
- Protologue: Fl. Javae Anonac.: 68 (1830).
- Family: Annonaceae
- Chromosome number: x= 9; P. longifolia, P. suberosa: 2n= 18
Origin and geographic distribution
Polyalthia comprises approximately 100 species and occurs in the tropics of Africa (about 6 species), Madagascar (18 species) Asia and Australia. South-East Asia is particularly rich in species. Polyalthia is found throughout the Malesian region.
Uses
In the Malesian region roots of Polyalthia are used in a decoction after childbirth and as an abortifacient, leaves are applied externally to treat skin diseases, and the bark is used as a febrifuge. Several other non-Malesian species are used in traditional medicine in Thailand: a decoction of P. cerasoides (Roxb.) Bedd. roots to treat fever and anaemia, and as a contraceptive for women and tonic for men, the roots or stems of P. debilis (Pierre) Finet & Gagnep. against abdominal pain, and a root decoction of P. evecta (Pierre) Finet & Gagnep. to treat abdominal pain and as a galactagogue.
The generally tough and flexible wood of Polyalthia is used for house building, interior trim, furniture, implements, packing cases, boxes, veneer and plywood. It is also suitable as firewood. The fibrous bark of several Polyalthia species is used to make rope. P. longifolia is planted as an ornamental.
Properties
The leaves and branches of P. suberosa contain suberosol, a C-31 lanostane-type triterpene, which inhibits the growth of human immunodeficiency virus (HIV) in vitro. An azaanthracene alkaloid has also been isolated from the stem of P. suberosa. The alkaloids 7,7'-bisdehydro-O-methylisopiline, 7-dehydronornuciferine, 7'-dehydro-O-metylisopiline and urabaine have been isolated from P. bullata stem bark.
Clerodane-type diterpenes with cytotoxicity against human tumour cell lines have been isolated from P. longifolia stem bark. The stem bark also afforded the cytotoxic aporphine alkaloid liriodenine. Extracts of P. longifolia showed antifungal activity against various plant pathogenic fungi, and were also found to be toxic to mosquito larvae.
Clerodane-type diterpenes exhibiting broad cytotoxicity against a panel of human cancer cell lines were purified from an ethyl-acetate-soluble extract of stem bark of the Philippine P. barnesii Merr.
The compound pyridine-N-oxide-2-thiolate (as zinc or copper complexes) has been isolated from roots of P. nemoralis Aug.DC., a species of Vietnam and southern China. This compound showed strong antimalarial, antimycotic and antiseptic activities.
In tests in India the alcoholic extract of P. cerasoides stem bark significantly prevented cold immobilization stress-induced changes in lipid peroxidation, ascorbic acid content in both brain and liver and vitamin E levels in the serum, suggesting it possesses antistress activity. The benzopyran derivative polyalthidin has been isolated from the stem bark of P. cerasoides; this compound showed potent biological activity as an inhibitor of the mammalian mitochondrial respiratory chain.
A labdane type diterpene with activity against the promastigote Leishmania donovani has been isolated from the stem bark of P. macropoda King from Malaysia.
In tests in Indonesia a chloroform extract of P. lateriflora (Blume) King leaves showed distinct insecticidal activity on Spodoptera litura; terpene compounds have been suggested as active compounds.
Botany
- Erect or sometimes scandent shrubs to fairly large trees.
- Leaves distichously alternate, simple and entire, glabrous or with simple hairs, pinnately veined, shortly petiolate; stipules absent.
- Inflorescence an axillary, extra-axillary or leaf-opposed fascicle or umbelliform raceme, flowers often solitary, often cauliflorous or ramiflorous.
- Flowers bisexual, 3-merous; sepals free or connate at base, valvate; petals 6(-8), free, often quite large and showy, equal or unequal, spreading, sometimes erect or cohering, leathery to fleshy; stamens usually numerous, cuneate, with orbicular or rhomboid connective concealing the anther cells; carpels 3 to numerous, free, style absent, stigma oblong, capitate or irregularly shaped.
- Fruit consisting of few to many, stalked or subsessile monocarps, fleshy, 1-5-seeded.
- Seeds with a longitudinal groove.
- Seedling with epigeal or hypogeal germination; cotyledons emergent and leafy or not emergent; hypocotyl elongated or not.
Early growth is reputed to be slow, becoming more rapid afterwards. Polyalthia develops according to Roux's architectural tree model, characterized by a monopodial orthotropic trunk with plagiotropic branches inserted continuously and with distichous leaf arrangement, flowering not influencing the architecture. Flowering can occur twice a year and flowers appear just before the new leaves. In general, Annonaceae fruits are eaten and dispersed by birds, mainly pigeons; fruits of P. longifolia are eaten and dispersed by bats.
Polyalthia is badly in need of revision. Some Polyalthia species from Africa have been placed in the separate genus Greenwayodendron, but this is still much disputed.
Ecology
Polyalthia occurs scattered as an understorey tree or shrub, or as a main canopy tree in primary or secondary lowland forest, sometimes in lower montane forest, up to 1200(-1800) m altitude. It is found in evergreen and monsoon forest, both on well-drained hills and poorly drained level sites. Individual species may occur as common elements of peat-swamp forest, occasionally also in "kerangas".
Management
Polyalthia can be propagated by seed, but germination is unpredictable. Seeds of several species showed 10-35% germination in 1-10 months in experiments in Peninsular Malaysia. P. cauliflora is highly vulnerable in the nursery, as the cotyledons and epicotyl are easily trapped in the testa and then rot. Sufficient watering and manual removal of the testa may resolve the problem. In natural forest the regeneration of Polyalthia is generally profuse.
Genetic resources
Some Polyalthia species have a rather narrow geographical distribution and face the risk of genetic erosion by deforestation.
Prospects
The numerous pharmacological tests showed many interesting properties of Polyalthia extracts, e.g. anti-HIV, antitumour, antifungal, antimalarial, antistress, antileishmanial and insecticidal activities. This certainly warrants more research, which may result in the development of modern drugs derived from these interesting medicinal plants. A taxonomic study of Asiatic Polyalthia is needed.
Literature
173, 581, 714, 785, 856, 883, 1048.
Selection of species
Authors
- R.H.M.J. Lemmens