mus'-tard (sinapi (Mt 13:31; Mr 4:31; Lu 13:19; Mt 17:20; Lu 17:6)): The minuteness of the seed is referred to in all these passages, while in the first three the large size of the herb growing from it is mentioned. In Mt 13:32 it is described as "greater than the herbs, and becometh a tree" (compare Lu 13:19); in Mr 4:32 it "becometh greater than all the herbs, and putteth out great branches." Several varieties of mustard (Arabic, khardal) have notably small seed, and under favorable conditions grow in a few months into very tall herbs--10 to 12 ft. The rapid growth of an annual herb to such a height must always be a striking fact. Sinapis nigra, the black mustard, which is cultivated, Sinapis alba, or white mustard, and Sinapis arvensis, or the charlock (all of Natural Order Cruciferae), would, any one of them, suit the requirements of the parable; birds readily alight upon their branches to eat the seed (Mt 13:32, etc.), not, be it noted, to build their nests, which is nowhere implied.
⇒See a list of verses on MUSTARD in the Bible.
Among the rabbis a "grain of mustard" was a common expression for anything very minute, which explains our Lord's phrase, "faith as a grain of mustard seed" (Mt 17:20; Lu 17:6).
The suggestion that the New Testament references may allude to a tall shrub Salvadora persica, which grows on the southern shores of the Dead Sea, rests solely upon the fact that this plant is sometimes called khardal by the Arabs, but it has no serious claim to be the sinapi of the Bible.
⇒See the definition of mustard in the KJV Dictionary
E. W. G. Masterman