Sunflower seeds are actually the fruit of the sunflower, especially when they are still in their hulls. Once the hull has been removed, what remains is the kernel (the part that we actually eat) so we can still call it a seed.
Paleo and PUFAs
Sunflower seeds are rich in fat and protein, but most of the fat is polyunsaturated, so be sure to limit your consumption. Polyunsaturated fats (PUFAs) are fine in moderation, but a diet high in them can lead to inflammation and elevated triglyceride levels. PUFAs are also unstable when exposed to heat and light, making them more likely to oxidize. Oxidized fats are dangerous because they can result in oxidized cholesterol in our blood stream and it is the oxidized cholesterol that latches onto our arterial walls, creating plaque and inflammation.
Micronutrients Found in Sunflower Seeds
Aside from fat and protein, sunflower seeds are also rich in various micronutrients, such as vitamin E and various B vitamins, particularly thiamine, niacin, folate, and vitamin B6. Sunflower seeds are also an excellent source of trace minerals such as magnesium, manganese, and phosphorous.
Mark Sisson talks about sunflower seeds in his list of edible seeds here.