Muntingia calabura (Jamaica cherry)

M. calabura is a small, fast-growing tree reaching 8-13 m in height, occurring widely in the lowland humid tropics up to 1500 m altitude. It self-seeds freely, regenerates rapidly under most soil conditions, including alkaline and saline soils, coppices well, and tolerates drought, shade and weeds.The small-dimensioned timber is used locally for general utility and fuelwood; in some areas it is used for pulp. The sweet berry is edible and is also eaten by birds and other wildlife (Verheij and Coronel, 1991). Non-wood uses include medicinal products, food, bark products, and honey. It seems suited for interplanting with agricultural crops, and also makes a good shade tree for livestock. A major disadvantage is that it is observed to be an aggressive colonizer of abandoned agricultural lands. The wide-spreading limbs tend to break in strong winds. As it is a pioneer species, research could be directed towards its utilization for the rehabilitation of marginal lands.

The seeds of M. calabura are dispersed by vertebrates that ingest the sweet juicy fruits. In a Costa Rican dry forest, at least 16 species (six species of birds, six of phyllostomid bats, two species of monkeys, one squirrel and one coati) are known to eat the fruits (Fleming et al., 1985). The bats Carollia perspicillata and Glosophaga soricina are the main nocturnal seed dispersers, along with the diurnal orange-chinned parakeet (Brotogeris jugularis).

In an urban area in Southeastern Brazil, 14 species of birds were observed consuming the fruits. The most frequent consumers were the sayaca tanager (Thraupis sayaca) and the plain parakeet (Brogoteris tirica) (Figueiredo et al., 2008). In urban Hong Kong, four species of birds, including the Japanese white-eyes (Zosterops japonicus) were recorded as fruit consumers (Corlett, 2005). In India, Thailand, peninsular Malaysia and Borneo, Muntingia fruits are commonly ingested by Cynopterus bats (Tan et al., 1998; Singaravelan and Marimuthu, 2006; Bumrungsri et al., 2007; Phillipps and Phillipps, 2016). Bats and green pigeons (Treron spp.) are thought to be primarily responsible for the presence of M. calabura in vacant building lots in Borneo (Phillipps and Phillipps, 2016).

In addition to vertebrates, fungus-growing ants may also possibly act as dispersers. In Southeastern Brazil, these ants were observed collecting the tiny seeds from fallen fruits and from bats and birds droppings (Figueiredo et al., 2008). Dispersal may also be influenced by rainfall drainage patterns. Seeds can be moved with water from the initial sites of deposition to the draining areas within the forests (Fleming et al.,1985). The species can be also easily propagated by cuttings and suckers (NAS, 1980; Sunshine seeds, 2016).

Accidental Introduction

M. calabura has been accidentally introduced in greenhouses/nurseries of USA, Spain and New Zealand via coco fibre imported from Sri Lanka (Hrusa et al., 2002; James et al., 2012; Ferrer Gallego and Laguna Lumbreras, 2013). In the Seychelles, it most probably arrived with the machinery used for the dredging and reclamation of the east coast of Mahé (Gerlach, 1996).

Intentional Introduction

M. calabura has been intentionally introduced in many Old World countries as a shade and fruit tree (NAS, 1980).

The chromosome number of M. calabura has been reported as 2n = 26 (Nevado and Ramirez, 1991), 2n = 28 (Bawa, 1973) and 2n = 30 (Löve, 1982). Nevado and Ramirez (1991) reported high pollen fertility (85.3%) and some chromosomal aberrations which include non-congression and early disjunction in metaphase I, and laggards in telophase II.

Growth and Development

Inflorescences are initiated by the growing shoot along with the subtending leaf, and develop along with this leaf, the fruit maturing shortly before the leaf falls. The flower fascicle is inserted supra-axillary, up to halfway along the internode. In the axil proper of the same leaves, side shoots are formed; these emerge before the inflorescence flowers, but extension growth is delayed until after the abscission of the subtending leaf. Under favourable conditions flowering fascicles are formed with every third leaf, but this may be delayed until the fifth, seventh or ninth leaf, or indefinitely. Side shoots are spaced further apart, but like the fascicles, they normally alternate along the branch. Thus growth and development are neatly structured at the shoot level, in a system which allows continuous extension growth and fruit production. Flexibility is afforded by varying the spacing of the fascicles, the number of flowers per fascicle and the sex expression of each flower.

Physiology and Phenology

M. calabura flowers and fruits all year round (Bawa and Webb, 1983; Webb, 1984; Fleming et al., 1985; Figueiredo et al., 2008), but the rate of flower and fruit production is not constant throughout the year. In Costa Rica, the flowering peak occurs at the end of the dry season (from April to May), while the fruiting peak occurs at the start of the wet season (from May to June) (Fleming et al., 1985). In Southeastern Brazil, the flowering and fruiting peaks occur from September to December, coinciding also with the end of the dry season and the start of the wet season (Figueiredo et al., 2008). In India, one flowering and fruiting peak occurs during monsoon season (July-October), and another peak takes place during winter-summer season (December-May) (Srikumar and Bhat, 2013).

Reproductive Biology

M. calabura starts producing flowers by the age of two years (Fleming et al., 1985). The flowers in a fascicle open sequentially at intervals ranging from 4-9 days. Within 2 weeks from the opening of the last flower, the first flower of the following fascicle may already reach bloom. A series of remarkable pedicel movements lifts each flower bud above the plane of the plagiotropic shoot just before anthesis and turns the flower to a pendant position within 2 days from fruit set.

The flowers, which are displayed above the branches, open at dawn and last only one day. They emit a weak sweet scent, and are visited by small and medium-sized bees, butterflies, hoverflies, ants, diurnal moths and hummingbirds (Bawa and Webb, 1983; Figueiredo et al., 2008). Bees appear to be the main pollinators (Webb, 1984). In an urban area in Southeastern Brazil, the stingless bee Trigona spinipes along with the African honey bee were the most frequent visitors (Figueiredo et al., 2008).

Flowers are bisexual, but very variable with respect to pistil size and number of stamens (Bawa and Webb, 1983). Within a tree, some flowers have a large ovary and very few stamens (less than 10), while others have a reduced ovary and many stamens (more than 100). Most of the flowers, however, are intermediate between these two extremes. Flower form strongly depends on the order in which flowers open in the cluster. Those that open first have larger ovaries and fewer stamens (Bawa and Webb, 1983).

Nectar is produced by all flower forms, although flowers with a large ovary and few stamens tend to produce higher quantities. The nectar can be classified as hexose-rich, which is the type used by small bees, and has similar proportion of sugars and other chemicals among the different flower forms (Bawa and Webb, 1983). It contains 13 different amino acids of which proline is the most abundant. Its production starts before dawn and continues until midday or early afternoon (Bawa and Webb, 1983).

Controlled pollination studies showed that this species is self-compatible, and that pollen is required for fruit production (Bawa and Webb, 1983). Although all flowers produce viable pollen and have the potential to produce fruit, fruit production varies significantly with flower form. Flowers with large ovaries almost always produce fruits, while flowers with reduced ovaries rarely produce fruits. Of all flowers with intermediate characteristics, ca. 50% produce fruits, which indicates that the probability of producing fruits is positively correlated with ovary size (Bawa and Webb, 1983). Once flowers are pollinated, the young fruits drop below the leaves, thus reducing the possibility of interference between pollinators and dispersers (Webb, 1984).

The fruits reach their maximum diameter (10-15 mm) at 40-60 days after pollination. Fully ripe fruits contain more water, carbohydrates and nitrogen, but less fibre, than green fruits (Fleming et al., 1985). They are consumed by birds, bats, monkeys and squirrels who disperse the several thousand seeds (see Natural Dispersal section). Germination tests showed that seeds that passed through the digestive tract of bats and birds germinate in similar proportions to seeds that were not ingested by animals (Fleming et al., 1985; Figueiredo et al., 2008), but those consumed by bats germinate faster (Figueiredo et al., 2008).

The seed is well-represented in the seed banks of forest soils and requires the high temperature and light conditions of large gaps in the forest for germination; the seedlings do not tolerate shade. Seeds germinate between 20 and 35°C. The optimal germination temperature was reported as 35°C (Leite and Takaki, 2001) or 25 °C (Lopes et al., 2002). Germination starts after 6-7 days and can continue for 35-40 days after sowing (Leite and Takaki, 2001; Figueiredo et al., 2008). Highest germination percentages and highest germination speed are obtained when seeds are subjected to prolonged white light exposure (more than 6 hours). Germination is inhibited under far-red light, and in the absence of light (Leite and Takaki, 2001; Lopes et al., 2002). Lopes et al. (2002) reported that seeds retaining their mucilaginous coat do not germinate, either in presence or absence of light.

Longevity

Fleming et al. (1985) estimated that the maximum longevity of M. calabura is about 30 years.

Population Size and Structure

The density and spatial distribution of trees of M. calabura appears to depend strongly on the site disturbance history and on the foraging activity of dispersers. In a Costa Rican dry forest, Fleming et al. (1985) reported 160-4,500 stems/ha in recently disturbed sites with a large availability of light gaps (e.g. along roadsides). In older, less disturbed forests, the tree density was low (1-5 trees/ha) (Fleming et al., 1985).

Associations

In the Neotropics, M. calabura is often associated with other early-successional tree and shrub species including Ochroma pyramidale (Malvaceae), Cecropia spp. (Urticaceae), Trema spp. (Cannabaceae), Piper spp. (Piperaceae), Casearia spp. (Salicaceae) and Luehea spp. (Malvaceae).

Environmental Requirements

M. calabura is a full sun species that grows best in a humid tropical climate (NAS, 1980). High temperatures and light conditions are necessary for seed germination, and for the development of seedlings, which are highly shade-intolerant (Fleming et al., 1985). It can grow on most soil types, both acid and alkaline, and even on poor substrates, but tends to prefer well-drained and sandy soils (NAS, 1980; Morton, 1987) and a pH of 5.5-6.5. In the Caribbean, Muntingia is commonly found on well-drained limestone. In the Pacific islands, the species has been recommended for planting on sandy coral soils (NAS, 1980). Lopes et al. (2002) reported that the best substrate for germination is sand.

The optimal temperature range for its successful growth is 22-32°C. The tree is sensitive to frost, but can withstand occasional low winter temperatures, for example in Florida (Morton, 1987). The most favourable range of mean annual rainfall is 1,400-2,000 mm, but the plant tolerates 1,000-2,400 mm (Useful Tropical Plants, 2016). It is also resistant to drought and to air pollution (Morton, 1987) but salt tolerance is poor.

A number of bioactive compounds, mostly flavonoids (flavones, flavanones and flavans), have been isolated from the roots, bark, wood, leaves and flowers of M. calabura. Extracts containing these compounds have been reported to have antioxidant, antimicrobial, anti-inflammatory, antidiabetic, anticancer, hypotensive and antipyretic properties among others, so the species has great potential for the development of plant-derived drugs (Kuo et al., 2014; Mahmood et al., 2014). Muntingia might also be exploited as a source of insecticide and fungicide. Hexane and alcoholic extracts from flowers and fruits exhibited strong insecticidal activity against the diamondback moth (Plutella xylostella), one of the most difficult pests to control (Bandeira et al., 2013). A formulation developed from the roots showed inhibitory activity against the fungal pathogen Alternaria solani, which produces the early blight disease in tomato and potato (Rajesh et al., 2014).

The wood pulp has potential for the production of cellulose (NAS, 1980). A granular biomaterial prepared from a mixture of leaves, fruits and twigs was effective in the removal of cationic dyes from dye-contaminated waters (Santhi et al., 2009). The fruits have been tested for ethanol production with Saccharomyces cervisiae and Schizosaccharomyces pombe (Thangadurai et al., 2014).

Social Benefit

M. calabura is commonly planted as an ornamental shade tree, and for its edible sweet fruits, which are eaten raw or cooked into jams and preserves (NAS, 1980; Morton, 1987). The berries are sold in local Mexican markets and are very popular in the Philippines with children. In most cases it is not a plant cultivated for its fruit and they are usually gathered from spontaneous trees (Janick and Paull, 2008). Different parts of the plant are used for medicinal purposes in several countries (Mahmood et al., 2014). The leaves are also used to make a tea-like beverage (Morton, 1987; Useful Tropical Plants, 2016). The bark yields a tough fibre that is used for twine, ropes and baskets, and in the construction of rural houses (Smith, 1965; NAS, 1980; Morton, 1987). The lightweight wood is utilized in carpentry, domestic utensils, and for fuel (Morton, 1987; Useful Tropical Plants, 2016). When thoroughly dry, the wood "ignites quickly producing a high flame with little smoke" (NAS, 1980). In Brazil, the fruits are said to serve as bait, "attracting fish for the benefit of fishermen" (Morton, 1987).

Muntingia is also a suitable shade tree for livestock (NAS, 1980), and is used as fodder/forage for cattle and goats in the Philippines (Calub, 2003). It is a melliferous plant. It has been reported as one of the species most commonly found in the pollen loads of honeybees in the Philippines (Payawal et al., 1991), and in the honey from a coffee-growing region of Northern Colombia (Montoya-Pfeiffer et al., 2014). It is also used in rituals (purification baths and cleansings) in the Afro-Cuban religion (Quiros-Moran, 2009).

Environmental Services

As an early successional species, M. calabura contributes to the regeneration of forests by creating the conditions for the establishment of middle and late successional species. Due to its ability to grow on denuded lands and to tolerate air pollution, this species has been considered as a candidate for reforestation projects (Morton, 1987).

The flowers are attractive to a wide range of pollinators. The fruits provide food to a number of diurnal and nocturnal vertebrates, including hummingbirds. In Brazil, Ruschi (2014) reported that the blue chinned sapphire (Chlorostilbon notatus) sucks the sweet juice of fruits in a similar fashion to nectar feeding. The fruits are so prized by these hummingbirds that the males aggressively defend the plants against intruders (Ruschi, 2014). Many species of insects, e.g. beetles, bugs, wasps and flies, also consume the pulp of ripe fruits (Fleming et al., 1985; Ruschi, 2014).

In Palau, it has been recommended to discontinue planting this species, and to consider eradication outside cultivation before it spreads further (Space et al., 2009).

Physical/Mechanical Control

Saplings and small plants can be pulled by hand, while larger plants can be uprooted using different tools (Koh et al., 2012). Tree girdling and stem cutting are not effective methods of control of this species (Koh et al., 2012), possibly because the plants may re-sprout.

Chemical Control

M. calabura can be successfully controlled by spraying the foliage with 41% glyphosate solution, but this method requires extensive safety measures and can affect non-targeted plants. Stem cutting combined with the application of 41% glyphosate solution on the stump sapwood is a better alternative, as well as the stem injection with 41% glyphosate solution (Koh et al., 2012).