David Mendosa says the answer is the macadamia nut.
Macadamia nuts
A great thing about the macadamia nut is that it’s one of the few nuts with a good omega-6/omega-3 fatty acid ratio. In other words, it’s high in omega-3 and low in 6. This may have important cardiovascular health implications. Macadamias are one of the nuts I recommend in the Low-Carb Mediterranean Diet and Paleobetic Diet.
David writes:
The first Australian macadamia plantation didn’t begin until the 1880s. And not until 1954 with the introduction of mechanised processing did commercial production became viable. Nowadays about 90 percent of the the world’s macadamia nut production comes from Hawaii, where it has become its third most important crop, according to The Wellness Encyclopedia of Food and Nutrition, University of California at Berkeley (1992).
Read the rest, where you’ll learn that macadamia nuts are the highest of all nuts in calories, gram for gram.
Macadamia nuts on the tree
Diabetic Mediterranean Diet 
Love macadamia and have several fun posts to boost her popularity 🙂 – http://cookupastory.wordpress.com/2014/01/21/miss-hawaii-takes-the-crown-three-cheers-for-macadamia/
I think this is where the whole o3/o6 ratio proves incredibly reductionist and short-sighted; mac nuts lack the natural density of other nuts with less favorable o3/o6 ratios. Almonds, ounce for ounce are much higher in magnesium, riboflavin and Vitamin E, and almost as high in manganese. Mac’s do have a higher amount of manganese and thiamin, but that is about it. Close examination reveals the mac to be one of the least nutritionally dense common nuts, far behind hazelnuts, pistachios, and even cashews. If you’re attempting to squeeze as much nutrition into your diet, mac nuts aren’t really the way to go, especially if your diet is calorie restricted.
Thanks for you input, william.