Interesting post Ginger
The PFAF web database page for PFAF - Arum maculatum has some info:
Mrs Grieve in her famous ( still great resource!) 'A Modern Herbal' states:
Tuber - cooked and used as a vegetable[2, 177]. A mild flavour, the root contains about 25% starch. A farina can be extracted from the root. Roots can be harvested at any time of the year, though they are best when the plant is dormant[K]. At one time, the tubers of this plant were commonly harvested and used for food, but they are very rarely used nowadays[268, K]. The root must be thoroughly dried or cooked before being eaten, see the notes above on toxicity.
Leaves - must be well cooked. Available from late winter. Caution is advised, see the notes above on toxicity.
The Arum has large tuberous roots, somewhat resembling those of the Potato, oblong in shape, about the size of a pigeon's egg, brownish externally, white within and when fresh, fleshy yielding a milky juice, almost insipid to the taste at first, but soon producing a burning and pricking sensation.The acridity is lost during the process of drying and by application of heat, when the substance of the tuber is left as starch. When baked, the tubers are edible, and from the amount of starch, nutritious. This starch of the root, after repeated washing, makes a kind of arrowroot, formerly much prepared in the Isle of Portland, and sold as an article of food under the name of Portland Sago, or Portland Arrowroot, but now obsolete. For this purpose, it was either roasted or boiled, and then dried and pounded in a mortar, the skin being previously peeled.
The 'Early Purple Orchid (Orchis mascula) is an altogether safer option which has similar characteristics to arrowroot for culinary use. In fact it has abundant mucalige, starch sugar and protein. It is also used medicinally for abdominal catarrhs and diarrhoea. Like other wild plants it is protected by the 'Wildlife & Countryside Act 1981, Section 13'( including Arums also and you can not remove the roots without the landowners permission) which means that you need the landowners permission before gathering the roots (different laws apply for fruit flowers and foliage under common law).
As with any wild plant they should only be gathered sparingly and only where they are abundant locally.
"He who would travel happily must travel light." - Antoine de Saint-Exupery. French aviator & author 1900 - 1944