Q. Is the mustard seed the smallest of seeds?
A. In Matt 13:31-32 Jesus calls the mustard seed “smaller than all other seeds,” but full-grown, would be big enough for birds to nest in its branches. But we know that there are seeds smaller than the mustard seed. E.g. the orchid seed is almost dust-like. And can a mustard seed ever grow into a tree big enough to hold a bird nest?
Jesus was not comparing the mustard seed to all other seeds in the world, but to seeds that a Jewish farmer might have “sowed in his field,” a key phrase in v31. And it’s absolutely true that the black mustard seed (Brassicanigra = Sinapisnigra) was the smallest seed ever sown by a 1st-century farmer in that part of the world. And, believe it, the black mustard seed in Israel will typically grow to 3.7 meters!
The Bible often uses everyday terms to share simple truth. Even today, we refer to a “sunset” when, technically, scientifically, we know that the sun never actually “sets”; it’s the earth that revolves.
In Matt 13 Jesus was addressing a local lay audience, not an international conference of botanists. No reasonable person would insist that this text provides a viable basis for questioning either Jesus or the Bible, when it comes to getting the facts straight—scientifically, historically, or technically.