Likely, Jesus meant the seed of the black mustard plant (Brassica nigra or Sinapis nigra), which is only about 0.039 to 0.063 inch [1 to 1.6 mm] in diameter.
Tõenäoliselt mõtles Jeesus musta sinepi taime (Brassica nigra või Sinapis nigra) seemet, mille diameeter on vaid 1 kuni 1,6 mm.