Pimenta dioica
(allspice)

P. dioica is a small evergreen tree native to the West Indies. It has been spread throughout tropical regions through trade as an ornamental species and for its spice known as allspice (Rodriguez, 1969). P. dioica is listed in the Global Invasive Species Database (ISSG, 2012), the Global Compendium of Weeds (2012) and is 'likely to cause significant ecological or economic harm in Hawaii and on other Pacific Islands' (PIER, 2012a). It is a priority species for exclusion from the Cook Islands (Space and Flynn, 2002a), Palau (Space et al., 2009), and Samoa (Space and Flynn, 2002b). It is listed a top invasive plant species on Bermuda (Brown, 2008; Copeland, 2011), Hawaii (Staples et al., 2000; Hawaii State Alien Species Coordinator, 2012), and Tonga (Space and Flynn, 2001).

Seeds are spread by fruit-eating birds (Staples et al., 2000), and potentially also via bats, lizards and insects (Rodriguez, 1969). Being an aggressive species, it has the potential to outcompete native plants (Space and Flynn, 2001). It is currently unknown how to best manage P. dioica invasion as the full potential threat to native species is not yet well understood: public awareness and discouragement of planting in natural, moist, lowland areas is advised (Starr et al., 2003) alongside removal from native forested areas (Space and Flynn, 2001).

P. dioica was first discovered in Jamaica by Spanish explorers around 1494, and trees were later discovered in Cuba, presumably dispersed there by migratory birds from Jamaica (Rodriguez, 1969; Parthasarathy et al., 2008). However there is some dispute over its exact origins (Parthasarathy et al., 2008). 

Trees are also found in Central America: Mexico, Honduras, Guatemala, Costa Rica (Parthasarathy et al., 2008). P. dioica has now been spread throughout tropical regions of the world through trade as an ornamental species and for its spice (Starr et al., 2003), including to India, Malaysia, South America and Pacific Islands (Rodriguez, 1969).

P. dioica is reported to be naturalized in Hawaii (Starr et al., 2003) and other Pacific Islands such as Tonga. There is disagreement over whether P. dioica is still present on Kwajalein (Kuwajleen) Atoll (Marshall Islands, Ralik Chain), but the most recent source states that is no longer present (PIER, 2012b).

P. dioica already widely occurs in warm regions around the world and has been present for many years in some cases (Starr et al., 2003). In Jamaica P. dioica is an economic crop, with exports of around 5,000 tonnes per year (Neal, 1965, via Starr et al., 2003). It is also a valued specimen and street tree. Because of its ornamental and economic value, it is likely that continued deliberate introductions by humans will occur. Seeds can be dispersed via birds (Staples et al., 2000), so it is likely that P. dioica will escape from cultivation and become established as a potentially invasive species once introduced.

New introductions are likely to affect island systems in particular, and the species is thought to pose significant risk to island flora due to its aggressive nature and ability to naturalize (PIER, 2012a). For example on Tonga, it is widely naturalized and in one area on ‘Eua it has been observed to form dense thickets of saplings: given this aggressive nature, the species is predicted to become a major threat in the future (Space and Flynn, 2001).

However, P. dioica has not always persisted in new regions it has been deliberately introduced to, and so may not threaten habitats unless conditions are favorable for reproduction and establishment (Rodriguez, 1969).

P. dioica is not listed as a quarantine pest, however it is a priority species for exclusion from the Cook Islands (Space and Flynn 2002a), Palau (Space et al., 2009), and Samoa (Space and Flynn, 2002b).

No specific details of habitats affected by P. dioica invasion other than geographical location (country) are available. Countries where P. dioica is present and invasive are within its broad temperature and rainfall tolerances (Parthasarathy et al., 2008).

Genetics

The basic chromosome number for the genus is x = 11 and Pimenta dioica is a diploid with 2n = 22.

There is a lot of variation in allspice with regard to yield and essential oil content, and on Jamaica there are many varieties, including dwarfs; some varieties produce many berries whilst others do not. Mexican trees have larger berry size, but yield is lower (Rodriguez, 1969). Two seedling variant types with dwarf/semi-dwarf habit and bushy nature are being conserved in the Indian Institute of Spices Research. The leaves of these variants are around 1/3 smaller than normal allspice leaves, and because of the bushy form with many branches, they may offer potential for crop improvement programs (Parthasarathy et al., 2008).

Reproductive Biology

Germination occurs after 9–10 days and continues over a month. There is some discrepancy over when trees become fully fruit bearing: Parthasarathy et al. (2008) states that trees grown from seed flower after 5–6 years, and take 18–20 years before becoming full bearing trees, whereas Rodriguez (1969) suggests full bearing is achieved between 25–35 years.

The time and extent of flowering is affected by local conditions and climate, particularly the onset of spring rains (Parthasarathy et al., 2008), and this can mean that flowering times can vary spatially within short distances such as between different sides of an island. Seeds germinating in the wild may take up to 10 years before flowering and fruiting. Full bearing can last for many years, over 100 for exceptional trees (Rodriguez, 1969).

Seeds can be dispersed by fruit-eating birds (Starr et al., 2003) as well as lizards, bats and insects (Rodriguez, 1969). Space and Flynn (2001) indicate that germination success is high, having observed ‘dense mats of seedlings’ growing under the parent tree; P. dioica seed production is >1000/m² (PIER 2012a).

Some trees can be barren, but the cause of this is currently unknown. Barren trees do however have a higher concentration of oil in their leaves. The species does not readily thrive outside of Jamaica and Grenada, possibly due to reproductive processes when certain critical environmental factors are absent, or in an unbalanced or unsatisfactory state (Rodriguez, 1969).

Environmental Requirements

In general, P. dioica is tolerant of a wide range of rainfall, temperature and altitude within tropical areas. It can grow from sea level to 1000 m and annual rainfall of 100–200 cm and mean monthly temperature of 27°C are preferred (Thankamani et al., 1994). It is somewhat selective over soil type, requiring free-draining coarse soil preferably in limestone areas. Soil type is thought to affect reproductive output, and is a possible reason why outside of Jamaica and Grenada the species is not as productive (Rodriguez, 1969).

Leaf rust caused by Puccinia psidii is the most serious disease of Pimenta dioica in Jamaica, first recorded in 1932. Young leaves, shoots, flowers, and young fruits are covered by bright yellow powder (parasitic fungal spores) in infested trees. Severe infestation results in defoliation, with successive attacks over 3-4 years leading to the death of the tree (Rodriguez, 1969). Leaf rust can be observed on both upper and lower surfaces of leaves, and mature leaves can bear brown lesions also covered with fungal spores (Parthasarathy et al., 2008). Puccinia psidii is native to, and present throughout, Central and South America as well as the USA (Florida, Hawai’i and California) (EPPO, 2012), and has a limited number of host species including rose apple (Rodriguez, 1969); Puccinia psidii has potential for use as a biological control agent of Pimenta dioica, but field trials are needed (Rayachhetry et al., 2001), and spores cannot develop in hotter temperatures of low altitudes (Rodriguez, 1969).

Pimenta dioica is also affected by die back or canker, caused by the fungus Ceratocystis fimbriata. The disease is usually localized and spreads to other parts of the tree. Infected trees display bark canker, dark streaks in the wood, and drying of leaves (Parthasarathy et al., 2008). Trees die within a few months when primary infection occurs low in the tree trunk, compared to infection via the branches (Rodriguez, 1969). C. fimbriata is widely distributed throughout the Americas, Europe, Africa, Asia and Oceana, but it is unclear as to whether it is native or introduced (EPPO, 2012).

In India, severe leaf rot between May-September has been caused by Cylindrocladium quinqueseptatum. (Parthasarathy et al., 2008). The larvae of red borer Zeuzera coffeae have also been reported to cause damage to trees, but this species of moth only occurs in Asia and Oceana (Parthasarathy et al., 2008; EPPO, 2012). The tea mosquito Helopeltis antonii has been also reported to attack Pimenta dioica in India, causing lesions on young shoots (Parthasarathy et al., 2008). This species only occurs in Asia, and is a minor pest of Pimenta dioica (EPPO, 2012).

Termites and ants have also been reported to damage trees due to nest building, and carrying other pests such as scale insects which attack the tree (Rodriguez, 1969).

Drugs, stimulants, social uses

• Stimulants

Environmental

• Biological control
• Ornamental

General

• Botanical garden/zoo

Human food and beverage

• Spices and culinary herbs

Materials

• Essential oils
• Oils
• Pesticide
• Wood/timber

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Furniture

Sawn or hewn building timbers

• Fences

P. dioica is a distinctive species, but care should be taken in the field to avoid confusion with P. racemosa (the bay or bay rum tree): P. racemosa has elliptical leaves with finer venation, slightly larger fruit and a five-lobed calyx (Neal, 1965; Bailey and Bailey, 1976 both via Starr et al., 2003).

P. racemosa (the bay or bay rum tree) is a related species of P. dioica, but P. racemosa can be distinguished by having elliptical leaves with fine venation, slightly larger fruit and a five-lobed calyx (Neal, 1965 via Starr et al., 2003; Bailey and Bailey, 1976 via 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.

It is currently unknown how to best manage the invasiveness of this species, as the full potential threat to native species is not yet well understood; public awareness and discouragement of planting in natural, moist, lowland areas is advised (Starr et al., 2003) alongside its removal from native forested areas (Space and Flynn, 2001).

Starr et al. (2003) stated that ‘P. dioica is likely controlled by herbicide applications using frill or cut stump methods’, but no specific herbicides are mentioned.

There is very little detailed information concerning the invasiveness of P. dioica. Few sources explain how the species is invasive (invasion mechanisms) and its impacts on other species, habitats or ecosystem functioning; empirical studies into the effects of P. dioica presence on native flora could not be found. There is also very little information surrounding the management of the species once it has become established, and only brief mention of how invasion may be prevented. More information on the factors affecting its reproductive success would be useful.

04/12/12 Original text by:

Isabel Jones, Consultant, UK