Purple top or Hokkaido turnips

Use what you like.

Remember that the primary responsibility for any cook is to put food on the table that will please his/her taste buds and the guests who will be joining at that table.

This isn't a strict recipe that will fail miserably if you don't follow it word for word like a Gospel. You are roasting veggies (turnips here) and tossing with a pretty simple French-inspired vinaigrette. Sub in different vegetables. Use boiled or steamed one. Or grilled.

Just do what you think will taste best with whatever you have/want.

Best of luck.