One of the mysteries of the English language finally explained.
Definition of black sage in English:
black sage
noun
1Any of several tropical American shrubs used (especially formerly) medicinally; especially Cordia curassavica (family Boraginaceae).
2US either of two blue-flowered plants of the family Lamiaceae (Labiatae) native to western North America, Trichostema lanatum and Salvia mellifera, both important as honey plants.
Origin
Mid 18th century; earliest use found in William Hillary (1697–1763), physician.