Iris brevicaulis Raf. has been found in Essex Co., Ontario, and could occur in southernmost Michigan, It would resemble I. virginica somewhat, but have six-angled capsules and a ± zigzag stem. Many other Iris are cultivated to varying degrees and could escape.
1. Plants dwarf, the flowering stems less than 15 (usually less than 10) cm tall.
2. Sepals with a prominent beard above; rhizomes stout (much more than 5 mm thick).
2. Sepals beardless; rhizomes slender (less than 5 mm thick most of their length).
1. Plants more than 15 cm tall.
3. Styles club-shaped, not concealing the stamens; sepals and petals alike; seeds round and shiny-black.
3. Style branches broad and petal-like, concealing the stamens; sepals and petals similar (the sepals larger, ± recurved, though petaloid in color and texture); seeds dull brown, flattened in common species.
4. Sepals with a prominent median beard above.
4. Sepals without a prominent beard, at most minutely pubescent.
5. Stems hollow; widest leaves 6–8 mm wide.
5. Stems solid with spongy parenchyma; widest leaves often greater than 8 mm.
6. Flowers yellow; outer spathe bracts smooth; fully mature capsules pendant.
6. Flowers blue (white in rare albinos), outer spathe bracts clearly mealy-papillose, especially apically (except in the rare escape Iris ×vinicolor); fully mature capsules erect (rarely somewhat spreading).
7. Sepals 2.5-5 cm wide; capsules six-angled; rare escape from cultivation.
7. Sepals 1.5-2.5 cm wide; capsules 3-angled; common native species.
8. Base of expanded portion of sepal with a bright yellow spot, finely pubescent with hairs as long as the thickness of the sepal; outer spathe bracts of uniform texture and color; seeds round to D-shaped, irregularly (but shallowly) pitted.
8. Base of expanded portion of sepal at most with a greenish yellow spot, with papillae shorter than thickness of the sepal; outer spathe bracts with the margins generally darker and more shiny than the rest of the dull surface; seeds D-shaped, with a ± regularly pebbled surface.