Who knew how powerful watercress really is as a vegetable? The relatively unpopular vegetable tops a new list of "powerhouse fruits and vegetables" with Chinese cabbage and chard landing in second and third respectively, according to a new study.

The results are from research examining so-called superfoods believed to be rich in nutrients. Scientists say there had been no scientific statement noting foods such as nuts, spinach or blueberries as superfoods.

Researchers at William Paterson University, in N.J., aimed to establish a classification system for defining protein density scores for vegetables and fruits and the results are a bit surprising.

Watercress tops the list of 41 'powerhouse fruits and vegetables' (PFV) due to its nutrients, content of fiber, potassium, protein and calcium.

"This study is the first of its kind to define and rank powerhouse fruits and vegetables," lead researcher Jennifer Di Noia, an associate professor of sociology, told LiveScience. The research was published in the journal Preventing Chronic Disease.

Romaine lettuce landed in eighth place with parsley taking seventh place. At the bottom of the list are pink and red grapefruit, sweet potatoes and blackberries.

"The proposed classification scheme is offered as a tool for nutrition education and dietary guidance," the authors wrote in the study.

"Nutrient profiling is not new," said Di Noia.  "But applications to fruits and vegetables are limited. This is the first classification scheme of which I am aware to define and rank" powerhouse fruits and vegetables."

In an published interview Di Noia explained the ranking is a nutrients-to-calories ratio "that expresses the mean of percent daily values for the qualifying nutrients the food provides per 100 calories. So higher-ranking foods provide more nutrients-per-calories."

What may be even a bigger surprise to those watching what they eat is that fruits didn't score so well. The top fruit was red pepper with tomato and lemon following on the list.