Try to make your search as simple as possible:
Luzula will find all items including that sequence of letters.
Search results for "Luzula":
"Luzula albida" - Luzula luzuloides
"Luzula maxima" - Luzula sylvatica
"Luzula maxima Marginata" - Luzula sylvatica Marginata
"Luzula nemorosa" - Luzula luzuloides
"Luzula purpurea" - Luzula elegans