Tuesday, 13 February 2018

Chestnut a surprising product of aquatic sedge

While on the subject of pseudo-cereals (but not superfoods), as I was last week, what about Water Chestnut? You will have guessed already that it's not a true chestnut (a species of Castanea), or even a horse chestnut (Aesculus hippocastanum), but something that might just grow in water.

In fact there are two edible plant products sold under this name. 'Chinese' Water Chestnut (above) is the corm ('bulb') of a sedge called Eleocharis dulcis, while what is sometimes also known as Water Caltrop (below) is the seed of a Lythrium (Loosestrife) relative called Trapa natans. Both grow in wet places.

The Water Caltrop is considered by Bohuslav Brouk, in his Plants Consumed by Man, to be a pseudo-cereal. According to Brouk, although the seed has been used since Neolithic times, today the fruits holding the seeds have more currency, as 'curios and souvenirs'. (I should add that this 1975 book was savaged at the time in many reviews, including this summary in the journal Economic Botany: '...[a] non-book, such a pretty package of misinformation, such inadequate coverage under such a grand title and pretentious jacket "blurb"...)

In Australia I've only seen the Chinese Water Chestnut for sale. In China the corm of Eleocharis dulcis is used in many dishes, often raw, although it has the attraction of remaining crunchy even when cooked. Yet despite its common name, Eleocharis dulcis grows naturally in many countries, including Australia. It has a tropical to subtropical distribution through much of Asia, across to Madagascar.

As Kathy Stewart and Bob Percival record in Bush Foods of New South Wales, the Chinese Water Chestnut is used by Aboriginal people in Australia, with old corms roasted and younger ones eaten raw. The stems are also used, to help in heal and seal open wounds. Magpie geese, also part of the diet of Northern Australian Aboriginal communities, graze heavily on this plant.

For more information on the Chinese Water Chestnut I eschewed Bohuslav Brouk in favour of Circular No. 956 put out by the USA Department of Agriculture in 1955... There I learn that the sedge is grown like 'paddy rice' in the south and east of China, where it is (or was) mostly called Matai, meaning 'horse's hoof'. The common name in English, Water Chestnut, is presumably a reference to the similarity of the corms to tree chestnuts.

To the USA palette, in the 1950s, the prepared Chinese Water Chestnut had a 'crisp, white, applelike flesh ... both sweet and starchy'. Uncooked it tasted to some like fresh coconut. Cooked it became a textural addition to omelets, macaroni and cheese, stews and the like. Small corms could be pickled, or fed to chooks.

And then there are the medicinal claims. For these I had to search beyond the USA Agricultural circular. There are claims that Chinese Water Chestnut has health benefits such as 'antimicrobial effects on bacteria, antioxidant activity, inhibition of inflammation and treatment for pharyngitis and laryngitis'. Indeed a recent study found that extracts from the peels of Chinese Water Chestnut, usually discarded during preparation, could be 'potentially used as a ... food supplement [for the] ... control or elimination of food borne pathogenic bacteria'.

Not bad for a plant of rather simple structure, essentially a collection of long green tubes. There are some 200 species of Eleocharis, with quite a few yet to be documented from South America (where most known species occur naturally). I can't think of any other Eleocharis species cultivated or appreciated in a similar way to Elecharis dulcis, although other sedges are of course used for thatching, basket-making and paper (e.g. Cyperus papyrus).

Images: habit shot of Eleocharis dulcis by Christian Fischer (CC BY-SA 3.0) and hosted by Wikipedia; images of corm by me; image of Water Caltrop fruit from Speciality Produce website.


Anonymous said...

Very interesting Tim. I remember showing both of these to students and visitors to Kew. There were some quite ancient specimens and varieties of Trapa Natans in boxes in the economic botany collections housed under the Sir Joseph Banks building. JOHN Ellison

Tim Entwisle said...

Thanks John. The whole field of 'economic botany' is something we should do more of at botanic gardens. And the collection at Kew is none to shabby... Tim

Anonymous said...

Hi Tim. Yep, none too shabby, yet I feel that in addition to the species of direct use and their landraces investigated by the likes of CGIAR and stored in numerous seed banks globally and in the global seed bank in Svalbard, while the Millennium Seed Bank at Wakehurst Place finally started preserving cross over species between those wild species collected for conservation and those which looked to be of potential use as a means of obtaining another large grant to carry on their existence; It seems to me that given our likely need to take advantage of any ecosystem service opportunity as the pressure of increasing population collides with the carrying capacity of our planet, that all nations should be investing far more effort in both sustainable futures and in preserving what exists while it is still there. This includes knowledge of the uses of ecosystem services by both indigenous peoples and innovations based on current science.

Tim Entwisle said...

True. We need the genetic resources and the knowledge about how to use them. The crop and the crop relative streams tend to run independently in most countries - certainly the case here in Australia. We do talk but the collections don't intersect in the way you suggest.