Fennel seeds are the dried seed of the fennel herb, and look like cumin seeds, only greener. They have an aniseed flavour and a warm, sweet aroma. They can be used on their own or in spice mixes such as Chinese five-spice powder and Indian panch puran.
Mustard seeds are the small round seeds of various mustard plants. They are an important spice in many regional foods and may come from one of three different plants: black mustard (Brassica nigra), brown Indian mustard (B. juncea), or white/yellow mustard (B. hirta/Sinapis alba).