Taxonomic name: Miconia calvescens D.C.
Synonyms: Cyanophyllum magnificum Groenland 1859, Miconia magnifica Triana 1871
Common names: bush currant (English), cancer vert (French), cancer vert, miconia (English), purple plague (English), velvet tree (English)
Organism type: tree
Miconia calvescens is a small tree native to rainforests of tropical America where it primarily invades treefall gaps and is uncommon. Miconia is now considered one of the most destructive invaders in insular tropical rain forest habitats in its introduced range. It has invaded relatively intact vegetation and displaces native plants on various islands even without habitat disturbance. Miconia has earned itself the descriptions “green cancer of Tahiti" and “purple plague of Hawaii". More than half of Tahiti is heavily invaded by this plant. Miconia has a superficial root system which may make landslides more likely. It shades out the native forest understorey and threatens endemic species with extinction.
Miconia calvescens is a woody invasive shrubby tree capable of reaching 15m in height; however the majority of specimens in the Society Islands are 6 to 12m tall, with slender, vertical stems (Meyer 1996). The leaves are opposite, elliptic to obovate, usually 60 to 70 cm long (sometimes up to one meter long). A prominent feature of the leaves is the three prominent longitudinal veins. The bicolorous form of the plant has dark green leaves on top with iridescent purple undersides. The inflorescence is a large panicle comprised of 1000 to 3000 white or pink flowers. Berries are 6-7 mm in diameter and purple to black coloured when ripe.
coastland, natural forests, planted forests, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, wetlands
Miconia calvescens thrives in tropical montane climate regimes; it is capable of establishing in areas that receive at least 1800-2000 mm of rain per year. It grows in lowland to montane tropical rainforest at altitudes between 300 and 1800 meters. Preferred microsites include mineral soil, dead tree boles and dead tree fern trunks.
Miconia is one of the most destructive invaders in insular tropical rain forest habitats. It is a serious threat to ecosystems in the Pacific because of its ability to invade intact native forests. Miconia has earned itself the descriptions such as the “green cancer” of Tahiti and the “purple plague” of Hawaii. Once miconia is established at a certain place it drastically changes the ecosystem and biodiversity of that environment.
Physical disturbance: Invasion by miconia has eliminated native forest understorey vegetation, increasing rapid runoff and potential for soil erosion and landslides on steep slopes.
Modification to Hydrology: Dense stands of miconia may damage watershed functions; there may be a significant change in the water balance, with an increase in runoff and a potential reduction in groundwater recharge, but this plausible result has yet to be fully investigated and documented (Burnett et al. 2006).
Economic/Livelihoods: Potential (as yet hypothetical) losses from an invasion of miconia on Oahu to groundwater recharge may conceivably be as high as $137 million per year (Kaiser and Roumasset 2002, in Burnett et al. 2006). Increased sedimentation could likely incur surface water quality damages; potential costs for Oahu have been estimated to be almost $5 million per year (Kaiser and Roumasset 2000, in Burnett et al. 2006). Comparable damage is possible on other Hawaiian islands, though the greatest economic impact is likely to be on Oahu, where 85% of Hawaii’s population is located.
Agricultural: Control programs underway since about 1995 have prevented significant agricultural impacts in the Hawaiian Islands. Invading miconia in ranchland near Hana, Maui in 1995-2000 was successfully removed. Theoretically, runoff from miconia stands could trigger erosion and loss of agricultural soil fertility (Chan-Halbrendt et al. 2007), but this has not yet happened or at least has not been documented.
Competition: When compared with a large group of native species M. calvescens appears to be better suited to capture and use light, which is consistent with its rapid spread in Hawaiian environments (Baruch Pattison & Goldstein 2000). Invasive characteristics of the species include rapid growth, fairly early maturity (after four years or more), production of large quantities of fruits and seeds, and effective seed dispersal by birds.
Threat to Endangered Species: In Tahiti, 70-100 native plant species, including 35-45 species endemic to French Polynesia, are directly threatened with extirpation by invasion of miconia into native forests (Meyer and Florence 1996).
Hawaii is home to a great number of rare and endemic plant, bird and invertebrate species at risk of global extinction, including over 350 federally endangered species. Upper Kipahulu Valley of Haleakala National Park on Maui, Hawaii, is a prime stronghold of Hawaiian biodiversity, containing stands of ohia (Metrosideros polymorpha) and koa (Acacia koa) that provide the primary habitat for rare native Hawaiian plants, birds and insects. Proactive response of Haleakala National Park personnel originally triggered a community-wide response to the miconia invasion in Hawaii about 30 years after M. calvescens had first been introduced to the State.
Also known as Miconia magnifica in horticulture, miconia has attractive bicoloured foliage and enormous inflorescences comprised of panicles of up to 3000 white or pink flowers that made it a highly attractive ornamental plant. When the alarm was raised against miconia in Hawaii in 1991-1992 (e.g. Gagné et al. 1992), all 1000+ spp. of the genus Miconia were declared noxious and prohibited under Hawaii’s Noxious Weed regulations, with the aim of preventing problems with other species in the genus. The entire family Melastomataceae is considered notorious for its perceived high percentage of invasive members (Meyer and Medeiros 2010).
- Miconia calvescens is referred to as miconia in this species profile which should not be confused with the genus Miconia.
- Invasions of Tahitian rainforests by M. calvescens dramatically accelerate after damage and disturbance caused by cyclones (Merlin & Juvik 1995, in Murphy et al. 2008b).
- There are 15 invading melastomes described for Hawaii (Almeda 1990, in Baruch Pattison & Goldstein 2000), including the forest tree M. calvescens, the shrub Clidemia hirta, and the herbs from open sites, Arthrostema ciliatum and Tibouchina herbacea (Baruch Pattison & Goldstein 2000).
- According to botanists studying the tropical Americans miconia "never […] occurs in monospecific formations" in its native region (F. Almeda, in a letter dated November 1988 to P. Birnbaum, in Meyer 1998b); this is in stark contrast to its growth form in introduced regions. P. Morat (director of the Laboratoire de Phanerogamie of the Natural History Museum of Paris) considered that, with only some 40 herbarium specimens present in Paris, this species has been little collected and in its native countries "is obviously a very banal species" (letter dated September 1988 to J. Florence, in Meyer 1998b)
Native range: Miconia calvescens is a tree native to Central and Southern America, from southern Mexico (20°N) to northern Argentina and southern Brazil (20°S) (Meyer 1994, in HEAR 2005; Meyer 1998); the bicolorous form is restricted to Central America (southern Mexico, northern Guatemala, Belize and Costa Rica) (Meyer 1998). In its native habitat miconia appears to be a shade-tolerant understory species that behaves as a pioneer tree in forest gaps (Meyer 1994, 1996).
Known introduced range: Miconia has been introduced outside its native range and is now considered one of the worst invaders of especially tropical insular habitats such as Hawaii, the Society and the Marquesas Islands and New Caledonia. Miconia is known to be naturalised in the rainforests of Sri Lanka, and occurs in numerous small populations in north Queensland rainforests in Australia where it is considered a serious potential threat (Murphy et al. 2008a, 2008b). Plants were also reported to be naturalised in Jamaica and to grow in the wild in Grenada (Lesser Antilles) and New Caledonia (Meyerson and Reaser 2003).
Introduction pathways to new locations
For ornamental purposes: Miconia calvescens has been introduced to new locations as an ornamental to public and private gardens followed by its escape and naturalisation (Meyer & Malet 1997).
Nursery trade: Miconia calvescens is a plant that was introduced to Hawaii by the floriculture and nursery industry (Chan-Halbrendt 2007). Miconia was brought into Hawaii in the 1960s as an ornamental plant for its aesthetic value; it was cultivated in Hawaii and sold in garden centers and nurseries until 1992 when it was placed on the noxious weeds list of Hawaii (Conant et al. 1997).
Other: Long distance dispersal by birds is suspected but unproven.
Taken to botanical garden/zoo: Miconia calvescens has been and is present in botanical gardens around the world.
Translocation of machinery/equipment: Transportation of dirty machinery and vehicles to the remote islands of Nuku Hiva and Fatu Hiva (Marquesas Islands, French Polynesia) is suspected to have spread Miconia calvescens. It was also introduced to the island of Tahaa (French Polynesia) in the early 1980s, probably with infested soil on the wheels of bulldozers used for road construction (Meyer 1998b).
Transportation of habitat material: Miconia calvescens seeds or seedlings may be transported along with soil to new locations (Meyer & Malet 1997).
Local dispersal methods
Consumption/excretion: Miconia calvescens fruits eaten and seed dispersed by frugivorous birds and rodents. Individual birds can carry thousands of seeds at least up to several kilometres.
Consumption/excretion: Fruits of Miconia calvescens contain hundreds of tiny seeds and are commonly consumed and excreted by birds and animals (Meyer & Malet 1997). In Tahiti, berries of miconia are ingested by frugivorous birds, particularly the introduced silver-eye (Zosterops lateralis) and the red-vented bulbul (Pycnonotus cafer), which transport and defecate the seeds (Gaubert 1992, in Meyer 1996). In Hawaii, dispersal is presumably by Japanese white-eye (Zosterops japonicus), common myna (Acridotheres tristis), the red-billed leiothrix (Leiothrix lutea) and perhaps northern cardinal (Cardinalis cardinalis) (Medeiros et al. 1997).
Garden escape/garden waste: Miconia calvescens has spread in the islands of French Polynesia (Tahiti, Moorea and Raiatea) where it was cultivated as an ornamental.
Hikers' clothes/boots: The tiny seeds of Miconia calvescens can adhere to mud on vehicles and shoes, including botanists!
On animals (local): Miconia calvescens seeds may get stuck on and be carried by the hooves of feral goats and pigs.
Road vehicles: Miconia calvescens seeds stick to the dirt/soil on wheels.
Translocation of machinery/equipment (local): Miconia calvescens may be spread on machinery, for example, machinery used for hydro-electricity (Tahiti), road construction (Marquesas Is.) or small water-tank construction (Austral Is.).
Water currents: Although most Miconia calvescens fruit falls beneath the parent tree, the seed is small enough to be dispersed by wind and water.
For a detailed account on the management of the spread of Miconia calvescens please read: Miconia calvescens (Miconia/Velvet Tree) Management Information. The information in this document is summarised below.
Preventative measures: A Risk Assessment of Miconia calvescens for Hawaii and other Pacific islands was prepared with a resulting score of 14, meaning it is likely to cause significant ecological or economic harm in the Pacific. Csurhes (2008) has prepared an assessment for Australia.
A range of fungi, weevils, leaf-feeding beetles, nematodes, wasps, butterflies and moths have been found in South and Central America which damage miconia. . In miconia’s invaded range in Hawaii, the non-native Chinese rose beetle (Adoretus sinicus) can cause up to 50% defoliation on individual leaves, but it has never been widespread and has never been observed to cause mortality (Medeiros et al. 1997). The high level of host specificity of the leaf-defoliating sawfly (Atomacera petroa) makes it a good potential control for M. cavescens (Badenes-Perez & Johnson 2007a). Since miconia seeds are dispersed by birds, fruit- and flower-eating insects including could help manage this weed (Badenes-Perez & Johnson 2007b). A fruit-feeding gall wasp (Allorhogas sp.) and a fruit-feeding beetle (Apion sp.) were evaluated for host specificity in Brazil by Badenes-Perez and Johnson (2007a). Other natural enemies (especially insects) are currently being sought in Brazil (since 1995) (please see Seixas Barreto & Killgore 2007 for further information), Costa Rica (please see Picanco et al. 2005 for further information), the Dominican Republic and Ecuador.
Legislation: Laws prohibiting the sale of Miconia calvescens in Queensland was passed in 1997 (Cshures 1998).
Education and Awareness: "Ho'ike o Haleakala" is an environmental education curriculum specific to Maui, produced by a partnership of school teachers, agencies, and community organisations, led by Haleakala National Park (Loope Starr & Starr 2004). The curriculum is available online (www.hear.org/hoike).
A growing interest of the public on Maui in meaningful hands-on ecological restoration projects is partially related to a growing interest in the heritage of the native Hawaiian people and proliferation of potential volunteer projects (www.hear.org/volunteer/maui/). Volunteers participate in a number of restoration projects, including one involving endangered dry forest plant species on private lands (Loope Starr & Starr 2004).
Campaigns to inform the public of the threat of miconia, including fliers and media coverage, were launched in the Society Islands (Meyer & Malet 1997).
Integrated management: Combining physical removal with chemical treatment has been employed to control miconia in the Society Islands. Trees (greater than four to five meters) were cut with a machete or a small chain saw and herbicide was systematically applied to the exposed stumps to prevent resprouting. After several trial with different herbicides, Gbnoxone (Triclopyr + 2,4-D) in diesel solution (one liter per 20 liters) applied carefully to cut stumps provided effective control with few resproutings compared with other chemicals used. 2,4-D is also said to be one of the most acceptable chemicals from an environmental point of view since it is not residual (Meyer & Malet 1997).
Miconia calvescens plants can tolerate otherwise poor growing conditions if adequate moisture is available.
The success of Miconia calvescens as an invasive plant is partly due to its prolific reproduction, with one mature tree flowering up to three times per year and bearing
up to 200-300 inflorescences that can produce more than 200 fruits each with 25 to 200 seeds per fruit (Medeiros et al. 1997; Meyer 1998a). Under favorable conditions, juvenile specimens can grow up to 1.5 meters per year (Meyer and Malet 1997) and reproduce when four to five years old (Meyer 1996). Full-sized trees (greater than eight meters tall) can flower two to three times a year and producing about two to three million seeds each time; flowering appears to be triggered by weather conditions (Medeiros et al. 1997). A young tree with only two panicles can produce ca. 200,000 seeds in its first fruiting season, whereas an older tree with over 50 panicles can produce over 5 million seeds per annum (Meyer 1998b). Production of a large amount of seeds and their remarkable longevity of up to 15 years or more (Meyer pers. comm., in Hester et al. 2010) results in the availability of seeds in the seed bank for germination when conditions are optimal. In addition, the large quantity of seeds enables easy dispersal by humans and other animals. Bird dispersal is overwhelming the most important mode of dispersal at the local level, but transport by humans has repeatedly led to large jumps in miconia distribution (e.g. Murphy et al. 2008b).
In a laboratory, some seeds germinate within 15 to 20 days when exposed to light and moisture, but others remain dormant (Meyer 1996). Data from Maui suggest that seed banks lie largely dormant under normal shaded conditions but are stimulated by the opening of the canopy (HEAR 2005). Laboratory experiments indicated that the seeds of M. calvescens are able to germinate in a large range of light conditions (even at 0.02 % of full sun and at R/FR = 0.5) but not in complete dark (Meyer 1994, in Meyer & Malet 1997). Moisture is a limiting factor and viability decreases rapidly when seeds are stored in dry conditions (Meyer 1994, in Meyer & Malet 1997). The soil seed bank may reach greater than 50 000 seeds/m². Longevity of the soil seed bank in Raiatea (French Polynesia) has been documented to reach at least 15 years (Meyer pers. comm., in Hester et al. 2010).
This species has been nominated as among 100 of the "World's Worst" invaders
Reviewed by: Lloyd Loope, USGS, Maui, Hawaii, USA
Compiled by: Profile revision: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Tuesday, 29 June 2010