The Sea Beet, also called Wild Spinach or Wild Beet, grows scattered on the European coast, for example in the Baltic Sea. It was temporarily considered strongly endangered, original holdings on Heligoland, for example, had become nearly extinct. Meanwhile, it recovers and spreads - presumable due to the milder winters - however, in recent years, along the Baltic coast, again.
The sea beet is considered the wild form and ancestor of a vast number of cultivated forms like the beetroot, the sugar beet, and chard. In spring, the leaves can not only be cooked but also prepared raw as salad, later - especially with rising temperatures - they develop a harsh off-taste and should only be prepared steamed or cooked like spinach anymore.
It's proven that it has already been used as a leaf vegetable by humans in the Neolithic period. Furthermore, it belongs to the earliest known crops and was cultivated in old Assyria, England, and Scandinavia, where it still belongs to the diet up to this day. Contrary to other cultivated forms, its root is consumable but very thin.