By Jason Hauser
Like Icecream bean, Peanut butter fruit and Madrono, the popular Malabar chestnut is probably one of the most readily confused and frequently mis-identified plant species in the nursery trade. There are at least 3 closely related but distinct species that fall under this common name Malabar chestnut, Pachira aquatica, P. insignis, and P. glabra. I have a number of these trees, all from different sources, and all look identical as seedlings and small trees. All were labelled under the species name “Pachira aquatica”. So far only one of my specimens has flowered and set fruit. it will be interesting to see what species the others will turn out to be as they come into fruit hopefully in the near future.
So which one might you have? Well your going to have to wait a while. The first real opportunity you will have to differentiate them is when you see the opened flower. The one featured in the pictures here turned out to be Pachira glabra! The following information, taken from CABI (https://doi.org/10.1079/cabicompendium.39237), will help you differentiate them when the opportunity arises:
Pachira aquatica → White to greenish flower petals, with bicoloured stamens that are white at the base and crimson towards the tips
Pachira insignis → Dark red to brownish flower petals, with bicoloured stamens that are crimson at the base and whitish towards the tips
Pachira glabra → Greenish flower petals, with white stamens from base to tip
Malabar chestnut, in all its forms, is commonly cited to produce an edible nut, but also the leaves and flowers are reported to have medicinal purposes. A quick perusal over various seller and perennial food growing web pages seems virtually unanimous in the verdict that they are edible. Trusting this advice I’ve have consumed in the past the odd nut from my trees here and there. Once removed from the rubbery seed coat and consumed raw the taste is somewhere between peanut and cashew, with a hint of macadamia nut. You can almost feel the high oil content as you mash it up between your teeth. Roasted (and slightly burned by error) the flavour does take on a more chestnut-like essence.
Since last year I’ve received warnings from trusted friends to do a bit more research on the edibility of this nut before I become a regular consumer. After all the common nursery tag like advice that gets spread around nowadays from web page to web page really isn’t worth the pixels its printed with. So before I potentially poison my future self I decided to do some extra due diligence! The following is a quick 30 minute dive into google scholar, which yielded some interesting findings.
The nut (of P. aquatica and P. insignis) is reported to be fed to pigs and cows, as well as eaten by people both raw, roasted and fried in areas of South America. Other part of the plant have been used medicinally in some regions of the world. (https://www.sciencedirect.com/…/pii/S0889157521000788)
A study assessing a number of different wild nut species for the purposes of human or animal consumption found that rats fed a diet of Pachira aquatica did not do well. Five out of six died, with notes to the effect of multiple organs being damaged, the surviving rat also had major organ damage. Whilst not directly comparable, this does raise some concerns. (http://www.sciencedirect.com/…/abs/pii/S0308814600000765)
A study assessing the potential of Pachira insignis nut oil for commercial food use found the nut contained high levels of cyclopropenoid fatty acids, and deemed it “unsuitable for food uses”. (http://www.sciencedirect.com/…/abs/pii/S0963996911004157)
Another study reported the presence of cyclopropenoid fatty acids, this time in Pachira aquatica. (aocs.onlinelibrary.wiley.com/doi/abs/10.1007/BF02657544)
One further study, this one with Pachira glabra as the subject, also found there was a high percentage of cyclopropenoid fatty acids, and commented that kernels of this species are not suitable for human consumption. (article.sapub.org/10.5923.j.fph.20120204.04.html)
So why the hysteria about cyclopropenoid fatty acids?
Well that did not become entirely clear with 30mins of research. But the gist I get is that there are a number of animal studies, mainly rats and chickens, that have shown it causes significant health problems, damaging organs and affecting the growth and development of offspring. There was also evidence found of probable carcinogenic or co-carcinogenic effects. Because of the negative effects reported in animal studies, there seems to be much caution around keeping the concentrations of these fatty acids to a minimum in human foods. But the actual influence on human health seems generally unknown, however one could assume at high enough concentrations it could be harmful.
So the verdict… it is unclear as to whether or not it is more carcinogenic to our health than a slice of crispy fried bacon!!
Given there are populations of people that consume these nuts, and there hasn’t been any clear evidence of human health troubles, consuming small amounts is probably not a high risk activity. Keeping the things that we do know in mind, I would not be labelling them as safe to eat in the interest of public safety. Personally I will continue to grow them due to their great hardiness, their amazingly scented flowers, and the lush tropical feel they contribute to the garden. I plan to investigate ways of preparing them that may reduce the risks of these potentially harmful fatty acids by inactivating them (and may still snack on the occasional raw one from time to time when I’m feeling a bit self-destructive!).
Happy responsible food consumption