Rhizomatous, with hollow stems often branched, and flat leaves. Flowers usually blue/purple with white patch of outer tepals, but other cultivars exist. Brown papery bracts when in flower. 

Other cultivated Iris may be found as garden escapes or deliberated planted - e.g. varieties and hybrids of Iris laevigata, I. spuria, I. versicolor, I. ensata. These have solid stems and bracts at least partly green at flowering (ref. Stace, 4th edn.)

Provide good quality photograph showing bracts and flowers, and note habitat.  

Pond margins and other marshy habitats, or rough ground

Occasionally planted by ponds in naturalising situations, or escaped from gardens

Occasional

Stace, C. (2019) New Flora of the British Isles (4th edn.). C & M Floristics