Sweetsop or Sugar Apple is a custard apple relative originating from lowland Central America and the Caribbean. It is now introduced and widely cultivated in other regions of the world, including South America, Southeast Asia, Africa, the Middle East and India.
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 crown. The bark is grey and fairly smooth, though it is sometimes roughened by leaf scars.
Leaves oblong to lance-shaped, 7 to 15 cm (2.5 to 6 in ) long, dull green and in an alternate arrangement along the branches. These fall off the plant in the dry season to conserve water, leaving the branches partly bare until the rainy season, which arrives with spring in its native range. Besides encouraging new leaves to grow, the rains cause the plant to flower.
Flowers oblong, 2 to 4 cm (0.8 to 1.5 in) long and made up of two sets of three petals, the inner set pale-yellow, the outer set yellow-green and leathery and neither set fully opening. They have both female and male parts and hang down on short stalks from the branches, where they attract 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 appear closely spaced but as the fruit ripens they ease apart and change colour, on green fruited varieties becoming medium green to a pale blue-green and the space between them turns a creamy orange. They are harvested when mature but still firm and range from 6 to 10 cm (2.5 to 4 in) in diameter or 200 to 400 grams (7 to 14 ounces) in weight.
The fruit is fully ripe when soft to the touch and is usually torn apart or sliced open with a knife then eaten fresh out-of-hand. The pulp is in segments that separate easily, each with a large glossy brown seed at the centre, and is sucked away in the mouth leaving the seed behind, which is then spat out and discarded.
The pulp, though 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 considered a poison risk if ingested.
The seeds are powdered and used as an insecticide and parasiticide in some countries, 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 17 to 25 °C, annual highs of 26 to 35 °C, annual rainfall of 700 to 4500 mm and a dry season of 2 to 8 months.
Trees may fail to produce flavoursome fruit in high altitude areas, where the average low of the warmest month is less than 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 and will do 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 a 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 to be low and probably results from poor pollination, due to the absence of the tree's native pollinators.
The fruit contain lots of seed, some of which scatter beneath the tree when the over-ripe fruit fall and splatter on the ground. Seed are also dispersed by animals, including birds that peck out the pulp and carry the seed a fair distance 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), but 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 project (HPWRA).
The leaves and ripe fruit fall to the ground creating litter and the seed have 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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