Try to make your search as simple as possible:
Pulegium will find all items including that sequence of letters.
Search results for "Pulegium":
"Mentha pulegium 'Nanum'" - Mentha pulegium Nanum low creeping form
"Mentha pulegium var. micrantha" - Mentha micrantha
"Pulegium vulgare" - Mentha pulegium