We observed Betelgeuse using ALMA ’ s extended configuration in band 7 ( f \approx 340 GHz , \lambda \approx 0.88 mm ) , resulting in a very high angular resolution of 18 mas . Using a solid body rotation model of the ^ { 28 } SiO ( \varv =2 , J =8-7 ) line emission , we show that the supergiant is rotating with a projected equatorial velocity of \varv _ { \mathrm { eq } } \sin i = 5.47 \pm 0.25 km s ^ { -1 } at the equivalent continuum angular radius R _ { \mathrm { star } } = 29.50 \pm 0.14 mas . This corresponds to an angular rotation velocity of \omega \sin i = ( 5.6 \pm 1.3 ) \times 10 ^ { -9 } rad s ^ { -1 } . The position angle of its north pole is PA = 48.0 \pm 3.5 ^ { \circ } . The rotation period of Betelgeuse is estimated to P / \sin i = 36 \pm 8 years . The combination of our velocity measurement with previous observations in the ultraviolet shows that the chromosphere is co-rotating with the star up to a radius of \approx 10 au ( 45 mas or 1.5 \times the ALMA continuum radius ) . The coincidence of the position angle of the polar axis of Betelgeuse with that of the major ALMA continuum hot spot , a molecular plume , and a partial dust shell ( from previous observations ) suggests that focused mass loss is currently taking place in the polar region of the star . We propose that this hot spot corresponds to the location of a particularly strong “ rogue ” convection cell , which emits a focused molecular plume that subsequently condenses into dust at a few stellar radii . Rogue convection cells therefore appear to be an important factor shaping the anisotropic mass loss of red supergiants .