Complex sentence: The very similar "Dietes grandiflora" (Large Wild Iris) is a larger plant, which can be distinguished by larger flowers which have dark spots at the base of the outer tepals, and last for three days.
Split into simpler sentences: The very similar "Dietes grandiflora" (Large Wild Iris) is a larger plant. It can be distinguished by larger flowers which have dark spots at the base of the outer tepals, and last for three days.