stiff aster: wiry tufted perennial of the eastern United States with stiff erect rough stems, linear leaves and large violet flowers
aster: any of various chiefly fall-blooming herbs of the genus Aster with showy daisylike flowers
passive immunity: an impermanent form of acquired immunity in which antibodies against a disease are acquired naturally (as through the placenta to an unborn child) or artificially (as by injection of antiserum)