Bitter Melon

Momordica charantia
Vine
Alternate
Simple
Yellow
Green

Bitter melon is an annual climbing vine probably native to tropical and subtropical Africa and Asia.  There are two botanical varieties viz.; M. charantia var. muricata (syn. var. abbreviata) and M. charantia var. charantia, the former mostly wild and the latter cultivated. The wild variety (M. charantia var. muricata) is considered as the progenitor of cultivated M. charantia var. charantia. M. charantia is a tropical and subtropical species belonging to the family Cucurbitaceae, and is widely grown for its edible fruit, which is among the most bitter of all fruits. 

Common names 
Also known as: bitter melon, bitter gourd, balsam apple, balsam pear;, bitter balsam apple, bitter cucumber, carilla gourd, paria, wild balsam-apple,
Family 
Cucurbitaceae
Deciduous 
No
Flowering time 
Can flower all year
Native/Exotic 
Exotic
Origin 
Tropical and subtropical regions on all continents. Possibly native to Queensland
Notifiable 
No
State declaration 
Nil
Council declaration 
NIL - Reduce
Known distribution 

 It is widespread in northern Queensland and vigorously competes with crops and native plants on the fringes of rainforests.

Habitat 

M. charantia grows under a very wide range of conditions throughout the tropics and subtropics. Its rapid growth and maturation allow it to colonize any area where there is sufficient short-term soil moisture, whilst it can also survive as a perennial in conditions of continuous soil moisture. It grows from sea level to over 1300 m, and in areas with annual rainfall as low as 480 mm. Minimum average annual temperatures may be as low as 12.5°C, though the plant is unlikely to thrive in such cold areas. It grows in soils with pH ranging from 4.3 to 8.7  M. charantia is a fast-growing vine and quickly covers the supporting vegetation or structure. In general, this species can be found growing in coastal areas, along creeks and rivers, forest edges and disturbed sites. For optimum growth, M. charantia needs a strong support, 1-4 m tall, however, it will also grow as a matted ground cover.

Habit 

Bitter melon is an annual climbing vine. There is a central taproot, from the apex of which the stems spread to climb over any available support.

Impact and control methods 

M. charantia is an aggressive invasive that grows as rapidly forming dense colonies that engulf native vegetation, climbing high into mature tree canopies and shading-out trees and shrubs in the understory. It competes for light and resources with native vegetation and it has the potential to completely out-compete vegetation communities by displacing native species, inhibiting the germination and establishment of seedlings in the understory and by changing community structures and altering ecological functions in invaded areas 

It is very invasive in Guam, and has also been reported as invasive in other parts of the Pacific, Brazil and the Caribbean. It interferes with the growth of a wide range of vegetables, annual, perennial, orchard and plantation crops by climbing over them, competing for light and possibly for nutrients and water, raising the humidity around their bases, and interfering with access, management and harvesting. It is a particular problem in sugarcane; in the first three months it may smother all growth, and at all stages, but particularly towards harvest it climbs over the crop and binds stalks together, reducing sugar content and making harvesting very difficult. For more information see the Queensland Government Fact Sheet

Stem and leaves 

There is a central taproot, from the apex of which the stems spread to climb over any available support. The well branched, slender, green stems are usually slightly 5-angled or ridged, and carry unbranched tendrils in the leaf axils. The leaves are carried singly along the stems on 3-5 cm long stalks, and each leaf is 4-10 cm long, rounded in outline, and deeply 5-9 lobed. The foliage has an unpleasant smell when crushed.

Flowers and fruits 

The flowers occur singly in the upper leaf axils on 2-10 cm long stalks with a small leaf-like bract towards the base. Male flowers have a slender basal swelling which is continuous with the base of the sepal tube, which ends in five blunt sepals. There are five oval yellow petals 10-20 cm long, and five central stamens. Female flowers are similar to the male flowers but have a distinct warty swelling well below the base of the sepal tube and three stigmas. Male flowers appear first and usually exceed the number of female flowers by about 20:1. The flower opens at sunrise and remains open for only one day.

The pendulous cylindrical fruits are egg-shaped and 2-10 cm long (up to 20 cm in cultivated varieties), and covered with longitudinal ridges and warts. At maturity, they turn orange to yellow, and the tips split into three and turn back to reveal the yellow pulp and the bright red arils that enclose the seeds which adhere to the inside of the fruit. Each of the flattened woody seeds is 5-9 mm long, and has finely pitted surfaces.

Reproduction and dispersal 

M. charantia spreads sexually by seeds and vegetatively by underground stems. The tips of the fruits split at maturity, and the sections curl backwards to expose the woody seeds embedded in sugary bright red arils. The arils are attractive to birds and animals which disperse the seeds. Seeds kept in dry storage remain viable for up to 24 months

Similar species 

There are many annual tendril-climbing weeds in the same family as M. charantia, none however, have the evil-smelling foliage, ridged and pitted fruit which turns yellow and splits open at maturity, and seeds enclosed in bright red juicy arils. M. balsamina is very similar except that it has bracts towards the top of the flower stalks and the fruits do not split open at maturity.