Try to make your search as simple as possible:
Hesperantha will find all items including that sequence of letters.
Search results for "Hesperantha":
"Hesperantha acuta" - Hesperantha rivulicola
"Hesperantha angusta" - Hesperantha bachmannii
"Hesperantha buhrii" - Hesperantha cucullata
"Hesperantha candida var. bicol" - Hesperantha longituba