Prickly pear. Often found on many Aegean islands and perhaps most abundantly in the Mani, where it grows over all the walls as mother nature's own barbed wire, and where they have recently started a juice company, En Mani, tempering the naturally sweet prickly pear juice with lemon etc. On Amorgos they make it into a kind of tequila.
Similar to the word for 'turkey', galopoula, the Greek word (literally the 'Frankish fig', ie 'Frankish' as anything from the Latin west. like Crusaders) reflects some confusion about the cactus's true origins. The French call it the figue de Barbarie, and Italians call it the fico d'India, but they actually come from Mexico and arrived in the Mediterranean thanks to the Spaniards, who brought them back in the early 16th century.
Images by Dr Peter Tzeferis, Creative Commons License, Victor Korniyenko, Creative Commons License