Iris germanica (Tall Bearded Iris). Grow from bulbs/rhizomes.There are hundreds of species with the majority blooming in spring & early summer. After 3-4 yrs. the clumps become crowded & don't bloom well. Dig them out & divide them to start new clumps.
There were simple purple and yellow iris in the flower bed in my secondary school. though not not. And then see more various of iris of different colour and shapes in UK ... Iris impression by Lord V on Flickr*