Try to make your search as simple as possible:
Xylosma will find all items including that sequence of letters.
Search results for "Xylosma":
"Xylosma balsamum" - Myroxylon balsamum
"Xylosma elliptica" - Xylosma panamensis
"Xylosma racemosa" - Xylosma congesta
"Xylosma salzmannii" - Xylosma prockia