Amaryllis atamasco.

Botanical name: 
Zephyranthes atamasca

AMARYLLIS ATAMASCO, L. Ground lily, Stagger grass. Said to poison horses and cattle, producing the disease called Staggers. Beautiful vernal white blossom.

Medical Flora, or Manual of the Medical Botany of the United States of North America, Vol. 2, 1830, was written by C. S. Rafinesque.