The Roman naturalist, Pliny the Elder, who died in 79 AD while investigating the eruption of Mount Vesuvius, writes: "Mustard grows entirely wild, though it is improved by being transplanted: But on the other hand when it has once been sown it is scarcely possible to get the place free of it, as the seed when it falls germinates at once."

Pliny describes in great detail the medicinal uses of the mustard plant, but it is important to remember that it was then, as it is now, a weed. It is significant that Jesus chooses a seed that when easily germinated tends to take over where it is not wanted, that can quickly get out of control and that attracts birds into a cultivated area, where they are least desired.