In the NKJV, Mark 4:31-32 reads like this: “It is like a mustard seed which, when it is sown on the ground, is smaller than all the seeds on earth; but when it is sown, it grows up and becomes greater than all herbs, and shoots out large branches, so that the birds of the air may nest under its shade.”

The rendering ‘the smallest seed in the world/earth’ is unfortunate and misleading. The Text has ‘of those on the ground’, repeating the phrase above it, only eliding the verb. The Lord was not making a global botanical statement, as the next verse makes clear—He was referring to vegetables planted in a garden in His day and in that area, and of such herbs mustard had the smallest seed. To object that tobacco and orchid seeds are smaller is beside the point. My translation reads like this: “It is like a mustard seed, that when it is sown on the ground is the smallest of all such seeds, yet when it is sown, it grows up and becomes larger than all the garden herbs and produces big branches, so that the birds of the air are able to rest in its shade.” The verb I have rendered ‘to rest’ is a compound form. The noun root refers to a temporary shelter, like a tent or a hut. The verbal form means to make use of such a shelter. Here the preposition κατα is prefixed to the verb, emphasizing, as I suppose, the temporariness. The Text says that the birds can use the shade, not the branches. But shade moves with the sun, and with the wind—how can you build a nest in something that keeps moving around (the Text actually says ‘under its shade’)? My comments also serve for Matthew 13:32, except that there the birds are resting in the ‘branches’, rather than the shade. The verb is the same, and I handle it the same way, ‘rest’ rather than ‘nest’, although ‘nest’ is possible.