mus'-tard (sinapi (Matthew 13:31; Mark 4:31; Luke 13:19; Matthew 17:20; Luke 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 Matthew 13:32 it is described as "greater than the herbs, and becometh a tree" (compare Luke 13:19); in Mark 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 (Matthew 13:32, etc.), not, be it noted, to build their nests, which is nowhere implied.
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" (Matthew 17:20; Luke 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.
E. W. G. Masterman