What it is
Not a nut at all — the small tuber of a sedge, the base of Spanish horchata de chufa, and a favorite grain-free, nut-free flour.
Why your biology objects
A tuber, so it sidesteps the seed and legume anti-nutrients — rich in resistant starch and fibre (prebiotic), with olive-oil-like monounsaturated fat. Possibly part of the early-hominin diet: *Paranthropus* dental and isotope work points to *Cyperus* tubers as a likely staple. Safe for tree-nut allergy despite the name.