'Mustard' in the Bible

It is like a grain of mustard seed which a man took and cast into his garden; and it grew and became a great tree, and the birds of heaven lodged in its branches.

But the Lord said, If ye have faith as a grain of mustard seed, ye had said to this sycamine tree, Be thou rooted up, and be thou planted in the sea, and it would have obeyed you.