Sweetsop or Sugar apple is a custard apple relative originating from lowland Central America and the Caribbean. Now introduced worldwide, it is grown for its fruit in South America, Africa, the Middle East, Southeast Asia, India and Oceania.
Sweetsop is typically a shrub or small tree 3 to 5 m (10 to 15 ft) tall, with one or more upright stems, off of which grow long lateral branches forming a wide-spreading, rounded canopy. The bark is grey and fairly smooth, though leaf scars sometimes roughen it.
Leaves are oblong to lance-shaped, 7 to 15 cm (2.5 to 6 in ) long, dull green and alternately arranged along the branches. These fall off the plant in the dry season to conserve water, leaving the branches bare to mostly bare until the rainy season, which arrives with spring in its native range. Besides encouraging new leaves to grow, the rains induce flowering.
Flowers are oblong, 2 to 4 cm (0.8 to 1.5 in) long and consist of two sets of three petals, the inner set pale-yellow, the outer set yellow-green and leathery, and none fully opening. They are bi-sexual, with female and male parts and hang down on short stalks from the branches, attracting pollinating insects.
The fruit are heart-shaped and with a lumpy surface of green bumps, less commonly purple, in a scale-like pattern. On young fruit, the bumps are closely spaced. As the fruit ripens, they ease apart and change colour, on green fruited varieties becoming medium green to pale blue-green, and the spaces between them creamy-orange. They are usually harvested when mature but still firm, ranging from 6 to 10 cm (2.5 to 4 in) in diameter or weighing 200 to 400 grams (7 to 14 ounces).
The fruit is fully ripe when soft to the touch and easily torn apart or sliced open with a knife and is commonly eaten fresh out of hand. The pulp is separated into segments, each with a large glossy brown seed at the centre, and is sucked away in the mouth, leaving the seed behind, which can then be spat out and discarded.
The pulp, although scant, is aromatic, with a custard-like, slightly granular texture and an agreeable sub-acid, somewhat musky flavour. Care is taken to avoid swallowing the seed, which some consider a poison risk if ingested.
The powdered seed are used as an insecticide and parasiticide in some regions, especially against lice infestation. The seed oil has also been shown to have an insecticidal effect on some insects.
The fruit pulp contains good amounts of Potassium and Vitamin B1 (Thiamine).
Sweetsop is the most drought tolerant of the cultivated custard apples, growing and fruiting best in sub-humid to humid subtropical and tropical climates, generally frost-free areas with annual lows of 14 to 25°C, annual highs of 24 to 35°C, annual rainfall of 700 to 4500 mm and a dry season of 2 to 8 months.
Sweetsop may fail to produce flavoursome fruit in high elevation areas, generally areas where the average low of the warmest month is below 18°C (64°F).
New plants are usually started from seed, which remain viable for years. However, they are slow to germinate, though this can be sped up by soaking them in water for a few days.
It performs best on free-draining loam and sand soils of a slightly acid to alkaline nature, generally with a pH of 6.5 to 8.0 and on sites with full sun exposure.
The root system is shallow, but the plant is surprisingly drought tolerant due to its habit of shedding its leaves during dry periods. It does well on thin soils, including gravel and stony soils, providing the roots are well mulched. It has poor tolerance to clayey, slow-draining, waterlogged or saline soils.
Hand pollinating is recommended to increase fruit-set and yield, which can be low due to the female and male parts of the flower maturing at different times of the day. Yields of 25 to 50 fruit per tree per year have been recorded for trees in southern Florida, which is considered low and probably results from poor pollination due to the absence of the tree's native pollinators.
The fruit contain many seed, some scattering beneath the tree when over-ripe fruit fall and splatter on the ground. Animals also disperse seed, including birds that peck out the pulp and carry the seed far from the parent plant.
It is listed as a weed in at least one reference publication and is recorded as naturalised in more than one country, including Australia, Brazil and the United States (Florida). However, there does not appear to be any record of it as a serious weed anywhere in the world. It is assessed as a low weed risk species for Hawaii by the Hawaii Pacific Weed Risk Assessment (HPWRA) project.
The leaves and ripe fruit fall to the ground, creating litter. The seed has poisonous properties, including being a strong irritant to the eyes if contact is made, such as rubbing the eyes after handling the seed.
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