Not all leafy greens are created equal - here's the definitive ranking of the best ones for you

Arugula's distinct taste doesn't quite correlate with high nutritional content. It's a good source of vitamins A and K but lacks in other nutrients that other greens boast.

Calories per cup: 6

Trendy for a reason, kale kills it in vitamin content, especially A, C, and K. Vitamin K is especially important in helping blood clot. But kale has one tiny downside: It's a tad higher in calories than other greens — though it's still very low! — which means that technically it has a lower nutrient density, the amount of nutrients packed into each bite.

Calories per cup: 33

Radicchio is a member of the chicory family. It packs in the vitamin K as well, containing more than 100% of your daily value.

Calories per cup: 9

Endive, also a kind of chicory, has its fill of vitamin K as well, and a cup has 20% of your daily vitamin A intake.

Calories per cup: 8

Romaine ranked among the top 10 "powerhouse foods," by the CDC, which are classified based on their associations with reduced risk for chronic diseases. It's an especially great source of vitamin A — one cup has 81% of your daily intake — as well as some B vitamins.

Calories per cup: 8

The most nutritious of the lettuce family, leaf lettuce is low in calories and high in potassium and vitamins A and K.

Calories per cup: 5

Spinach, the staple of any good fruity salad, is one of the top-ranking greens for its all-around nutrition content. It's packed with vitamins and nutrients, particularly potassium and iron, which are important for regulating your blood cells and blood pressure.

Calories per cup: 7

With its defining red stems, chard is among the top powerhouse foods because of its low-calorie, high-nutrient content. It had the most vitamin K of any leafy green on this list, at nearly 300% of your daily value per cup. Chard contains a fair amount of magnesium, which is important for things like muscle and nerve function, blood-glucose control, and blood-pressure regulation.

Calories per cup: 7

Watercress, with its little round leaves, was considered the top powerhouse food in the CDC study. It's high in vitamins A, C, and K and incredibly low in calories.

It's linked to a lower risk of type-2 diabetes and it's not too hard to grow.

Calories per cup: 4