heliotrope (n.)

"plant which turns its flowers and leaves to the sun," 1620s, from French héliotrope (14c., Old French eliotrope) and directly from Latin heliotropium, from Greek hēliotropion "sundial; heliotropic plant," from hēlios "sun" (from PIE root *sawel- "the sun") + tropos "a turn, change" (from PIE root *trep- "to turn"). In English the word in Latin form was applied c. 1000-1600 to heliotropic plants. Related: Heliotropic.