Yes, plants have to be included in the project. you need 20 plants. The only things you need to write about them I think is the plant name and the plant family. Its 10 marks of the project for all of them.
No there's no specific plants. You can really collect any I think. Some of the ones I've collected already are oats, thistle, nettle, meadow buttercup, Heather, ragworth, linseed, cleavers, silver wood and a few more