Leptocereus grantianus (sebucan) is a sprawling or suberect, nearly spineless cactus, reaching up to 2 meters in height and 3 to 5 centimeters in diameter.

The outer perianth segments are linear, green, and tipped by an areole like those of the tube and ovary.

Leptocereus grantianus is endemic to the island of Culebra which is located just off the northeastern corner of Puerto Rico.

Associated species include the sea grape (Coccoloba uvifera) and almacigo (Bursera simaruba).

The steep rocky banks are unstable and located close to the shoreline; therefore, natural events, such as hurricanes, might result in the complete elimination of the only known population.