Try to make your search as simple as possible:
Luffa will find all items including that sequence of letters.
Search results for "Luffa":
"Luffa aegyptiaca" - Luffa cylindrica
"Luffa astori" - Luffa operculata
"Luffa astorii" - Luffa operculata
"Luffa sphaerica" - Lagenaria sphaerica
"Luffa tuberosa" - Momordica cymbalaria