Macaranga tanarius
(parasol leaf tree)

Native to southeastern Asia, through to Australia and the western Pacific islands, Macaranga tanarius is a medium-sized tree that is cultivated in tropical regions throughout the world for a range of uses, including the production of timber, firewood, traditional medicinal products and shade. It is also used as an ornamental and in reforestation. As a pioneer species, M. tanarius is favoured by disturbance and rapidly colonizes gaps or margins in well-developed rainforest. In Hawaii, given its potential for rapid colonization and its ability to form dense stands, it is considered either an environmental weed or a potentially invasive cultivated plant threatening endangered native species.

In its native range, M. tanarius occurs from the Andaman Islands (India), southern China, Ryukyu Islands, northern Australia and Malesia to the west Pacific islands (Whitmore, 1980; Airy Shaw, 1982). It is a common species in mainland South-East Asia, including southern Thailand and peninsular Malaysia, and on Indonesian islands, including Sumatra, Borneo, Lesser Sunda Islands and Sulawesi, as well as New Guinea and the Philippine Archipelago (Purwaningsih and Sukardjo, 1991).

M. tanarius has been introduced to Singapore, the Marshall Islands and all the main islands of Hawaii, having become naturalized and invasive in valleys on Kauai, Oahu and Maui (Starr et al., 2003; PIER, 2015; Speith and Harrison, 2015).

Apart from Hawaii, M. tanarius is not listed as an invasive species in any of the regions outside its native range. However, given its uses as an ornamental and in reforestation projects, further intentional introduction of M. tanarius in the tropics is likely.

M. tanarius is limited to tropical and subtropical climates. As a fast-growing pioneer plant, it is often found growing in secondary forests and especially in cleared rainforests. Its spread is favoured by disturbance and so rapidly colonizes gaps or margins in well-developed rainforest (Australian Tropical Rainforest Plants, 2010). It is also found in thickets, brushwood, village groves, coastal rainforest and estuaries (Florabank, 2015; World Agroforestry Centre, 2015). M. tanarius occurs mainly in areas with a mean annual rainfall between 950 and 4000 mm, at altitudes from near sea level up to 800 m (Florabank, 2015). It grows in a variety of soil types including clay, loam and sand, and is fairly common in lowlands (World Agroforestry Centre, 2015).

A study by Tseng et al. (2003) indicated that the phytotoxins produced during leaf decomposition of M. tanarius inhibited the growth of Lactuca sativa, Bidens pilosa and Leucaena leucocephala. They concluded that the pattern of weed exclusion underneath stands of M. tanarius and its invasion into adjacent grassland vegetation results from allelopathic interactions.

Genetics

M. tanarius has a haploid chromosome number of 11 (Miller and Webster, 1966; Whitmore et al., 1970).

Reproductive Biology

M. tanarius is pollinated by insects and to a lesser extent by wind (Ishida et al., 2009), with flowering and fruiting occurring several times a year. It propagates by seed, with an average germination rate of 50% if the pulp remains on the seeds (World Agroforestry Centre, 2015).

Physiology and Phenology

Cotyledons of M. tanarius are broadly elliptic to orbicular, about 16 mm in diameter; upper surface hairy; undersurface sometimes bearing numerous small, yellow glands (Australian Tropical Rainforest Plants, 2010).

M. tanarius flowers and bears fruit fairly regularly (World Agroforestry Centre, 2015). In Australia it flowers from spring to summer and fruits mature in summer (Florabank, 2015). In Hong Kong, it is reported to flower from April to May and to fruit from June to August (Hong Kong Flora and Vegetation, 2012).

Longevity

Under cultivation, this species lives less than 15 years (Florabank, 2015). Under natural conditions, the lifespan is over 20 years, but as a pioneer species that quickly fills any gap that occurs in the forest canopy allowing light to penetrate to the ground, M. tanarius quickly disappears as the longer-lived components of the mature rainforest return.

Population Size and Structure

M. tanarius tends to form dense thickets that impede the growth of other vegetation, thus allowing it to form near monocultures.

Associations

This species is myrmecophilic: several ant species in the genera Crematogaster and Camponotus can serve as partners that sometimes colonize the trees (Guhling et al., 2005).

In Japan, M. tanarius is pollinated by the flower bug Orius atratus (Anthocoridae, Hemiptera), which breeds on the inflorescences (Ishida et al., 2009).

Environmental Requirements

M. tanarius is found in tropical and subtropical climates, from coastal estuaries to inland upland sites as high as 800 m above sea level (World Agroforestry Centre, 2015). It has been reported to tolerate temperatures as low as 6°C and as high as 34°C. When dormant, the plant can survive temperatures down to about 1°C (FAO, 2007). It tolerates different soil types including clay, loamy, medium and coarsely textured soils, either acid or neutral. It prefers a mean annual rainfall between 800 and 1200 mm, but tolerates 700 to 4000 mm. The species is sensitive to waterlogging and drought (Florabank, 2015). 

The potential damage by the bug Decomioides schneirlai, which feeds on M. tanarius’ floral nectar without contributing to the pollination of the plant, is regulated by the plant’s insect pollinator Orius atratus (Ishida et al., 2009).

When it suffers leaf damage from herbivory, M. tanarius produces extrafloral nectar on its shoots and leaves to attract predators and parasitoids, which reduce the number of herbivores on the plant (Heil et al., 2001).

Environmental

• Agroforestry
• Boundary, barrier or support
• Erosion control or dune stabilization
• Firebreak
• Revegetation
• Windbreak

Fuels

• Fuelwood

Materials

• Alcohol
• Bark products
• Dyestuffs

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical

Ornamental

• garden plant

Roundwood

• Building poles
• Posts

A similar species to M. tanarius in Hawaii is Macaranga mappa (L.) Mull. Arg., which is distinguishable from M. tanarius by its larger leaves (60-100 cm) and bracts, and pink calyx (Starr et al., 2003).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Public Awareness

The Big Island Association of Nurserymen in Hawaii has voluntarily agreed to not order or sell M. tanarius to prevent further spread. It has been classified as "High Risk" by the Hawaii-Pacific Weed Risk Assessment and should not be cultivated (Speith and Harrison, 2015). Starr et al. (2003) suggested discouraging the public from planting M. tanarius, especially near uncultivated areas or water bodies.

Eradication

Eradication techniques include hand-pulling or treatment with herbicide.

Cultural Control and Sanitary Measures

Control by use as firewood is unlikely, as this species has been reported as undesirable for charcoal production in the Philippines (Hyman, 1983). 

Biological Control

There are no known biological agents for the control of M. tanarius (Starr et al., 2003).

Chemical Control

In large wild stands, Starr et al. (2003) suggested cut stump or basal bark herbicide application as a possibly effective method for the control of M. tanarius. Foliar spray on taller individuals, however, may not be effective and is not advised in areas where non-target plants are present, although control methods suggested for dense stands in Maui, Hawaii, include aerial applications of herbicide via spray ball or herbicide ballistic technology (Maui Invasive Species Council, 2013).

Monitoring and Surveillance (Incl. Remote Sensing)

In the West Maui mountains, M. tanarius populations were mapped using helicopter surveys and ground surveying. This revealed that M. tanarius had a much larger range than was previously thought, and resulted in this species being added to the area’s priority invasive species lists (Maui Invasive Species Council, 2013).

09/07/15 Original text by:

Diana Quiroz, Wageningen University, Netherlands