The Collaborative International Dictionary of English v.0.48:

Sego \Se"go\, n. (Bot.)
   A liliaceous plant (Calochortus Nuttallii) of Western North
   America, and its edible bulb; -- so called by the Ute Indians
   and the Mormons.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Calochortus nuttallii
    n 1: perennial plant having clusters of one to four showy white
         bell-shaped flowers atop erect unbranched stems; edible
         bulbs useful in times of scarcity; eastern Montana and
         western North Dakota south to northern Arizona and
         northwestern New Mexico [syn: sego lily, Calochortus
         nuttallii]