A new and distinct cultivar of Chrysanthemum plant named `Yosonoma`, characterized by its upright, outwardly spreading and mounded plant habit; vigorous, strong and freely branching growth habit; dark green-colored foliage; uniform flowering response and habit; freely flowering habit; large daisy-type inflorescences with elongated oblong-shaped and purple-colored ray florets; and good postproduction longevity with plants maintaining good substance and color for about three weeks in an interior environment.