From the information I gathered today, parsnips are richer in vitamins and minerals compared to their cousins. And more importantly they're loaded with potassium (600 mg per 100 g). Carrots have only 50% of that amount (320 mg per 100g). Spinach comes in as a close second behind parsnips (560 mg per 100g).
Parsnips are not the same as Parsley Root. They look somewhat the same but are very different in taste apparently. I didn't know the difference until I went looking for parsnips earlier today and accidentally picked up parsley root.