I'd probably lump them in the 'modern palatable' category - they are cultivars and originate in Asia (fertile crescent region). They are drupes (edible seeds) - as are almonds, pecans and walnuts
A little except from wikipedia
"Like other members of the Anacardiaceae family (which includes poison ivy, sumac, mango, and cashew), pistachios contain urushiol, an irritant that can cause allergic reaction"
According to the cron-o-meter, they have 13.7 PUFA per 100g, of which 13.5g is O6
I tend to avoid them