Ariasema tortuosum unripe fruit, stem and leaves visible at bottom of photo.
The pea-sized unripe fruit of Arisaema tortuosum is eaten after washing, preserving in salt and cooking in North East India according to (apparently only one) report(1).There is also a report of the fruit (apparently ripe) being eaten after roasting (2). It is very rare to get edible fruit from a plant that grows in full shade like this one does. There is also a report that the peeled stem is edible, along with a warning to cook thoroughly to neutralize dangerous https://www.laura-selection.com/butchers-broom-shoots-what-a-delight/(3).
I could not find any advice on how long you need to cook it for. I sampled the unripe fruit raw (without swallowing), it produced the characteristic feeling of needles piercing the skin on the inside of the mouth typical of uncooked aroids due to calcium oxalate crystals.
I tried boiling a few stems, leaves and fruit for 1 hour with 3 changes of water. Even after this time there was still a slight numbness and tingling in the mouth from eating them, but I was not noticeably harmed from swallowing a relatively small amount. The peeled stems were particularly good, well worth the fiddly task of peeling them, the leaves tasted good, like spinach, and the few unripe fruit seemed non-descript.
It is unclear if longer cooking is required or if they are eaten despite the slight numbness and tingling they produce as has reportedly done with the bulbs of its relative Arum italicum during famine (3). There is a report that although the tubers are eaten cooked violent illness has been known to follow eating a large amount of them (4) which may indicate not all of the calcium oxalate crystals are neutralized by cooking and they are normally eaten in moderation.
Despite this plant's highly desirable ability to flourish in very shady locations I won't be eating much of it unless longer cooking, &/or other common techniques such as soaking and drying, prove to eliminate the slight numbing effect. Further experimentation will have to wait until next year's harvest.
A related plant, Zantedeschia aethiopica (arum lily), is a common weed here in Wellington. There are a few obscure references to the tubers being eaten by humans (Wildflowers of Transvaal. Cythna Letty 1962. & Food Plants of Southern Africa. Ashton Kim Ruiters. 2012). So I tried some. The tubers are large and fiber free, so look very promising. However I found even after many hours of cooking they still have a reasonable amount of calcium oxalate crystals causing a feeling of eating needles. Drying for maybe six months like some other aroids seems like the only remotely possible way of making them safe and pleasant to eat.
Another arum, Arum italicum, is a common weed in parts of Wellington. There are ethnobotanical reports the leaves are eaten after lengthy cooking (e.g. , The ethnobotany of wild vegetables in the Adriatic Islands. Luczag. 2019 et al. ) I found after 1 hour the unpleasant prickly sensation of calcium oxalate crystals was still very much there. After 3 hours of boiling with changes of water there was only a slight numbing, no prickly sensation, by this time it was almost a (tasteless) mush. Seemed safe to eat but even more cooking probably wise. Hard to see the point in going to the trouble of cooking for so long it unless nothing else is unavailable. I will be trying the tubers, which have been highly valued in North Africa.
References.
1) The Wild Edible Plant Diversity of North-East India. Ashish Kar. 2009.
2) An Ethnomedical Review on Arisaema tortuosum. Hemlata Verma, V K Lal, KK Pant and Nidhi Soni. INTERNATIONAL JOURNAL OF ADVANCES IN PHARMACY,
BIOLOGY AND CHEMISTRY Vol. 1(2), Apr- Jun, 2012.
https://ijapbc.com/files/03-125.pdf
3) A hundred years of change in wild vegetable use in southern Herzegovina. Lukasz Luczaj, Katija Dolina
https://docksci.com/a-hundred-years-of-change-in-wild-vegetable-use-in-southern-herzegovina_5a62c443d64ab2c4e6b71ff5.html
"The memory of eating Italian lords-and-ladies (Arum italicum Mill.) starchy bulbs during famine in World War II is still present, though there was no consensus on the proper detoxification technique (the plant contains large concentrations of oxalates which can harm the digestive tract). Some people remember it boiled, others roasted or fried. The processing did not completely remove the stinging feeling. Hungry people swallowed the bulbs in spite of the unpleasant feeling in the throat."
4) Edible Plants of North West Himalaya (Uttarkhand) Rakesh Shad. 2015.
