From the Vatican website announcement
(via Google translate, bold added):
...Pope Francis has decided to keep his coat front, chosen from his episcopal consecration and characterized by a linear simplicity.
The blue shield is surmounted by symbols of papal dignity, the same as those taken by his predecessor Benedict XVI (miter placed between crossed keys of gold and silver, bound by a red cord). At the top, stands the emblem of the order of origin of the Pope, the Society of Jesus, a radiant sun and flamboyant loaded from the letters in red IHS monogram of Christ. The letter H is surmounted by a cross, at the tip, the three nails in black.
Below, are the star and the flower of nard. The star, according to the ancient heraldic tradition, symbolizes the Virgin Mary, Mother of Christ and of the Church, while the flower of nard shows St. Joseph, patron of the universal Church. In the iconographic tradition Hispanic, in fact, St. Joseph is depicted holding a branch of spikenard. By placing these images in his shield, the Pope wanted to express his particular devotion to the Blessed Virgin and St. Joseph.