Where do cress seeds come from?

i'm growing some cress from a packet of seeds, but to enable me to keep growing it. where do the seeds come from, i don't ever recall seeing cress with flowers on it. So where do i collect the seeds from without having to keep buying more???

Where do cress seeds come from?
Cress is cultivated before it goes to seed. Leave some to go to seed.
Reply:Isn't it mustard?