Try to make your search as simple as possible:
Streptocarpella will find all items including that sequence of letters.
Search results for "Streptocarpella":
"Streptocarpella 'Sparkle'" - Streptocarpus Sparkle
"Streptocarpella holstii" - Streptocarpus holstii
"Streptocarpella saxorum" - Streptocarpus saxorum
"Streptocarpella saxorum 'Var." - Streptocarpus saxorum Variegated