Sweet Leaf (Sauropus androgynus)

I was on the tail of a butterfly for a photo, but it flew away, and now I’m sad that I can’t remember what it looks like in sufficiently explicit detail to identify it. On the bright side, I did end up finding a couple of these growing amongst the rusted rails, which were a nice surprise- I like tiny dangly fruits with pretty colours and shapes, and this one fit the bill perfectly.

sweet leaf fruits flowers

Female flower, and two semi-ripe fruit. Fruits on this particular cultivar ripened from a pale green through to a bright pink

As it turns out, it’s one of the most popular vegetables in Southeast Asia, although I’d never heard of it before. Anyhow- it’s often added to soups and salads, most commonly cooked in stir fries with eggs or beansprouts or anchovies. It can even be used as a food dye. Known as katuk, star gooseberry or sweet leaf, Sauropus androgynus is a tropical shrub with alternate leaves and can reach a height of 6m in the wild. Leaves are reportedly nutty or pea-like in taste, with a hint of asparagus. Its flowers are small, with six round sepals, and are monoecious, meaning that there are separate male and female flowers on the same plant. These are also edible, as are its fruit that look somewhat like mini mangosteens (or mini round lanterns, for those who aren’t familiar with the mangosteen). They contain black seeds, which are dispersed by explosive action. In some countries, they’re grown using shade cloth and fertilizers to produce shoots that are tender and have few leaves, which are then sold as ‘tropical asparagus’.

sweet leaf topview

Top view of the plant

Sweet leaf leaves are packed full of protein, vitamins, antioxidants and lutein (a pigment good for your eyes), and in folk medicine, are used against coughs, wounds, urinary disorders, to relieve fevers, and increase lactation (production of breast milk). In fact, many studies have been done, which do show that the leaves have anti-diabetic, anti-obesity, wound-healing, anti-inflammatory, antioxidant, antimicrobial, and lactation-inducing properties. Unfortunately, many forget the age-old Chinese adage: 是药三分毒, or in English, medicines are also poisons. In 1995, some vendors in Taiwan decided to ignore the reason why regulatory boards exist, and convinced people that the extract of raw sweet leaf was good for dieting. 278 people, who drank ground raw sweet leaf mixed with fruit juice, developed lung problems (known as bronchiolitis obliterans), with a number requiring lung transplants. Essentially, their bronchioles (the smallest branches of lung airways) were compressed, meaning that they would have had difficulties breathing since airflow would be obstructed. In 2005, the same problem happened in Japan. It is believed that the culprit is an alkaloid known as papaverine, which could induce two proteins known as TGFβ and eNOS, which in turn cause airway fibrosis (hardening due to deposition of fibrin, a protein), and epithelium destruction (destruction of the lining of the airway).

sweet leaf

Leaves shouldn’t be consumed raw. The bright pink fruit here is ripe, with a distinct dark pink calyx. Note the little flowers: the pink ones are female, and the cream coloured ones, like the one just beside the fruit and to the right of that same branch, are male

But for those who just want to grow it for its aesthetics, or to cook with, here’s some good news: it’s easy to grow. Native to the Indian sub-continent, China, Southeast Asia and Papua New Guinea, it can grow in both tropical and temperate climates, surviving temperatures of 5 to 38 degrees (Celsius), although it grows best when daytime temperatures fall between 26 to 35 degrees (Celsius). It prefers full sun to partial shade, likes acidic, well-drained soil, quite a bit of water, and can even tolerate the occasional flood. Propagation is simple, either with stem cuttings, or via seeds. Sure, it isn’t the most compact plant and can be quite leggy, but if you don’t mind a little artistic flair to cut through the monotony of clipped, uniform bushes, it really isn’t too bad a choice.

References

  1. http://tropical.theferns.info/viewtropical.php?id=Sauropus+androgynus
  2. http://www.eattheweeds.com/edible-katuk-sauropus-androgynus-2/
  3. http://www.npr.org/sections/thesalt/2014/08/14/340358325/sayur-manis-delicious-but-also-deadly-greens-from-borneo
  4. https://en.wikipedia.org/wiki/Sauropus_androgynus
  5. https://florafaunaweb.nparks.gov.sg/Special-Pages/plant-detail.aspx?id=2427
  6. https://www.daleysfruit.com.au/Herbs/sweetleaf.htm
  7. https://www.hindawi.com/journals/ecam/2015/714158/
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